I can play the piano, saxaphone, and guitar, and I've never considered being able to think about music to be actually hearing it.

I only learned that some people don't from the Mastodon thread - it's slightly disorienting finding out how differently other people's brains work. This, for you, might be like the day I realised that aphantasia was a thing and people weren't just using flowery language when they talk about visualising things.