In the same way that playing Guitar Hero is playing the guitar, yes.
No, in the same way that listening to Mozart's 40th symphony is listening to Mozart. You are very literally listening to Mozart if you're listening to his 40th symphony, much like you're very literally studying quantum mechanics if you're studying concepts of quantum mechanics. If you say that you were listening to Mozart last night, nobody thinks that you mean you listened to every single piece written by Mozart last night, they are probably going to assume that you just listened to his 40th symphony. Likewise, if you say that you were studying quantum mechanics last night, everyone will just assume that you studied a few basic concepts, not that you understand everything that there is to know about quantum mechanics now. If you say that you were playing the guitar last night and the truth is that you just played Guitar Hero, that statement is both factually false and misleading.
You're missing a difference in context and wording. What you're saying is accurate if the statement was "I was studying quantum mechanics". That's not the statement though. Here's what Kirian (mis)quoted:
"I taught myself quantum and nuclear physics last night"
Unlike your Mozart example, the context and wording here implies that the speaker started and finished the process in that one night. If he had started earlier, he would say "I finished teaching myself". If he had only started on some concepts but not finished, he would say "I taught myself
some" or "I was teaching myself". Or he would use the word you used, "I studied". These subtle differences matter and convey different meanings.
And pacovf made this correction(?):
In any case, we are discussing a misquote. Tony Stark becomes takes one night to become an expert in "thermonuclear astrophysics". I don't even remember if that field was relevant to the discussion in the movie.
I can't fully remember what Stark said exactly, but he definitely implied (or maybe explicitly stated) that he became an expert in a highly advanced field in a single night. And that's what people have been talking about.