Tocharian is a language, we don't know who the "Tocharians" were as the linked paper explains in the abstract (and then somewhat ignores). Strictly speaking we don't even know if they were one ethnicity, the Tarim Basin has always been a melting pot and even during the time of the Tocharian manuscripts there were already Sogdians (Iranians), Han Chinese and others living and trading there.
There also isn't really evidence that the mummies are directly linked to the later Tocharian speakers of the texts in the first place. They may be or may be not.
It should be noted that research in this field is extremely politicized within China even by local standards. The finding isn't surprising in the sense that this is what the official narrative is, so they found what they were looking for. Uyghurs, who don't have a local origin, claim the mummies as their ancestors but the Chinese state strongly denies this. There may be something to that story as it's generally assumed they intermixed with the local population when they settled there. When you visit the museum in Urumqi you're greeted by a sign claiming the area had always been Chinese.
If we assume a Western hypothesis, it's also possible that the mummy genes are "local" but the language isn't, if we were to assume the study findings are correct. There are dozens of other possibilities.
> Tocharian is a language, we don't know who the "Tocharians" were as the linked paper explains in the abstract
We do know that the Tocharians were a people [1], as they were identified as such by writings in Sanskrit, Greek, and Persian. But the Tocharian language is too late (400-1200CE) to make any connection to the Tarim mummies, which date to 1800BC.
However, the Tocharian language has distinctive features that suggest that it branched at a very early date (3000BC [1]) from the other Indo European languages, which would put its "origin" date far earlier than its attestation date, and possibly (though not provably) associated with the Tarim mummies.
The signals point both ways, and as you say, this was a diverse part of the world in ancient times, so it's impossible to know what language they spoke given current evidence. They could just as well have been multilingual.
> It should be noted that research in this field is extremely politicized within China even by local standards.
Yeah, this is very unfortunate, but common across Asia as countries form post-colonial national identities, but in doing so force complex questions about history and human migrations into the service of very simplistic nationalist identity narratives.
You see this particularly in India, where the nationalists in power reject (without basis) the entire notion that the Indo-European languages originated in Central Asia (i.e. Yamnaya culture). This is of course not to excuse the biases of colonial scholarship, which had its own serious problems in how it characterized linguistic and archaeological discoveries, allowing them them to be pushed into service of colonial nationalist narratives.
>Müller's identification became a minority position among scholars when it turned out that the people of Tokharistan (Bactria) spoke Bactrian, an Eastern Iranian language, which is quite distinct from the Tocharian languages. Nevertheless, "Tocharian" remained the standard term for the languages of the Tarim Basin manuscripts and for the people who produced them.[11][16] A few scholars argue that the Yuezhi were originally speakers of Tocharian who later adopted the Bactrian language.
And so forth. Not that Wikipedia is a reliable source in the first place but your link mentions a couple of competing theories, showing that we don't know - since all of it is speculation and unproven. Languages can be shared by people of different ethnicities. Many Europeans wrote texts in Latin and Greek despite being neither.
To be clear I completely agree with you regarding the language, which is well studied thanks to the many preserved texts. We just don't know much about the people, even the name that was given to them was retroactively made up.
There also isn't really evidence that the mummies are directly linked to the later Tocharian speakers of the texts in the first place. They may be or may be not.
It should be noted that research in this field is extremely politicized within China even by local standards. The finding isn't surprising in the sense that this is what the official narrative is, so they found what they were looking for. Uyghurs, who don't have a local origin, claim the mummies as their ancestors but the Chinese state strongly denies this. There may be something to that story as it's generally assumed they intermixed with the local population when they settled there. When you visit the museum in Urumqi you're greeted by a sign claiming the area had always been Chinese.
If we assume a Western hypothesis, it's also possible that the mummy genes are "local" but the language isn't, if we were to assume the study findings are correct. There are dozens of other possibilities.