Hello~!

Couple years ago, I went to Japan.. When I was checking in to get my ticket.
They checked by passport, ID and the booking details, then the customer service rep asked me to hold on and when to the back and talked to a manager... The customer service rep (which was my freind) came back to me and asked me what I did.... It seems like when the typed in my information in their system, I was flagged for some reason.

What can this be?
Does airlines do a background check before boarding??

Please l