No, you were mindreading (psychological definition), and you were wrong.

You don't need mindreading to detect the condescending tone. That was there, absolutely.

But you went further to suppose that you could infer my internal mental state; that's the mindreading part, and the part you didn't get right. I don't personally mind, but I think it's one of the biggest risk factors for an unproductive discussion, so I tend to point it out whenever I notice. (It is, of course, the easiest to know when someone's made a mistake about me, because I have privileged access to my own mental states.)