Is it normal to speak as someone else?

Quick background info: My ex and I have stopped speaking for about a couple weeks now, she told me she never wanted to speak to me again. She and I are both female, this was our first lesbian relationship ever, she said she was finished with girls completely after what she went through with me.

Now a few days ago I joined a lesbian chat site to try and get over my ex, sort of a distraction. The first day I met some pretty cool people there (all platonic) so went back the next day.

Came across this really awesome person, who made me feel really comfortable and just felt familiar to me, we ended up flirting and just talking. 2nd day we spoke again for hours, she finally told me her name (common name), then i gave mine (very unique name) she freaked out and then it hit me who she was or who i thought she was.

But she insists she's my ex's best friend (who also shares same name). I've never spoken to her or met her just have heard a lot about her. She flipped off at me for what i did to my ex. Told me a lot of things that i did'n't know, my ex crying, her not sleeping, how much i hurt her, how angry she was with me etc.

But the way she spoke, down the the phrases, shortening words, everything is exactly like my ex. I believe with 99% certainty it was my ex, but why would someone pretend to be someone else is the part that makes me doubt.

Is it normal someone would do that?