Guy acts pissed off when I mention other guy?

Guy this post is about: A

Guy i got shipped with: M

My friend (female) shipped me with M.
Told A about it later because we're pretty good friends and i found it funny. Instead he acted kinda confused, almost shocked. He seemed pissed and left pretty quick and we always talk for a bit after class
Guy acts pissed off when I mention other guy?
Post Opinion