...I think I might have seen something similar back home. Admittedly, I can't say for certain, since I don't know what your story is, but there were two people who looked identical to each other despite not knowing who the other one was and not being related. [Erza probably wouldn't be able to properly explain why that would be the case if she was pressed - most of what she knows comes second-hand, from friends who had been in Luceti briefly - but if she keeps it brief, she shouldn't have trouble.]