You're wrong about categories of analogy, but I don't blame you - analogies are a pretty slippery slopes. In particular, you're most likely conflating these because of the implementation detail - you write HTML, so writing music is an analogy. Not really - writing HTML is closer to performing music.
You can teach almost everyone to perform "Twinkle Twinkle Little Star" on piano or "Smoke on the Water" on guitar within 15 minutes, both of which are de facto "Hello world!" equivalents to many aspiring musicians.
EDIT: Removed attempt at drawing a HTML/music analogy which could be closer to truth. It is really fruitless endeavour, makes no sense.
I disagree. The rendering engine of the browser is the performer who looks at my script(HTML/CSS/JS) and produce the final result for the visitors to the web page. Writing HTML is not closer to performing music, but actually closer to composing music, if you will.
Also, I think although knowing theory would help you play a song with an instrument, it's not required, is it? More likely knowing music theory is for understanding/appreciation of the composition/structure of the music. So no, playing "Twinkle Twinkle Little Star" on an instrument is NOT equivalent to writing "Hello world!" program. On the other hand, composing a super simple but complete song is closer to writing a "Hello world!" (or a Fibonacci series) program.
You can teach almost everyone to perform "Twinkle Twinkle Little Star" on piano or "Smoke on the Water" on guitar within 15 minutes, both of which are de facto "Hello world!" equivalents to many aspiring musicians.
EDIT: Removed attempt at drawing a HTML/music analogy which could be closer to truth. It is really fruitless endeavour, makes no sense.