It's a lot more than theoretical that he was blowing smoke. It's almost certain that he was. Assange is personally aware of how to crack NTLM hashes. If there was any actual intent to crack that hash I'd expect to see a lot more follow up in the conversation... like "ok I'm running john/hashcat with the common word list... how about you upload the SAM/try mimikatz? What do you know about the local password complexity policy?", and stuff like that.. but there's none of it.

If "I'll ask a guy" is all that's required to make something into a conspiracy that is incredibly, mindblowingly flimsy.