Hm. I would have said ...vous vous êtes rencontrés...., i.e., use the reflexive form which requires être. That's a case for Cécile.

I'm glad I reviewed these questions/answers. I too did not read this as the use of the reflexive se rencontrer, but that Kwiz erred using etre instead of avoir. Perhaps this is one of those times that there should be an explanation of the "implication" as part of the written lesson. I'm quite sure there are others either getting the answer wrong or merely terribly confused.