Whether or not she remembers the exact incident doesn't mean it didn't sow doubt in her head at the time.
Sometimes when women are very emotional, the logic part of their brain kind of... dies? That sounds kind of sexist but it's the best way I can describe it. It happens with men, too, but with men it's mainly an anger thing. With women they experience the disorientation a bit more, in my experience.
My girl used to point out stuff I did in arguments, but the way she described it sounded way more insane than what I felt like I actually did. They sometimes remember it differently as well.

It's hard to say because your girl was not communicating properly with you, which will kill off any relationship, good or bad.
In this case, I don't feel like you really did anything wrong. If you didn't cheat then you didn't cheat, y'know? There's not much to it than that, but as men when we analyze our past behavior, it makes it easier for us to be aware of it in our next relationship. I'm the good partner I am now because of the women prior to my current girl.