Sounds to me like you were roleplaying just fine.

I think the sudden, abrupt change in playstyle threw the folks you play with off a bit. Sudden behavioral changes can be signs of severe stress or drug use so it may be that your GM just horribly missread the situation and his "you okay, dude?" got you a bit gun-shy.

That's my take anyway.

Anyhow, if you ever pretended to be a favorite character from a book, movie, or videogame when you were young, that's roleplaying. The only difference in an RPG is that you (presumably) made up the character you're pretending to be rather than drawing from some media you've consumed.