That's cool! It's a man-in-the-middle attack, except Alice is _expecting_ to talk to Eve but gets paired with Bob. "Man-on-both-ends attack". The English wizard Derren Brown used the same weird trick to defeat ½ of a group of grandmasters and a plant (I think it was Robert). IIRC there was a chatbot or something that did the same thing to spoof a Turing test, but I can't find anything about it; maybe it hasn't happened yet.
It seems like it would be very difficult to prevent this; I wonder what Tinder will do?