Sounds like a pretty big goof, when McCoy's a doctor for Pete's sake. (If he can figure out what they are at all, he ought to be able to call it by the right word.)
It is evident that Star Fleet's Medical Doctor program is of no higher standards than "Palamino Beach Upstairs Medical Correspondance School"! Remember, also, in the seventh season episode of DS9, the one where Ezri is trying to solve the case of the serial homicide killer, Dr. Bashir had no idea what "powder burns" were, when examining a shooting victim! This is even more surprising when you consider all the time he and O'Brien spend in the holodeck "re-enacting" the "War for Texian Independence"!!! (Oh yes...the spell-checker does not recognize that "Texian" is the correct term for the anti-SantaAna forces in the Texas Revolution...lol)
Yeah, it's the wrong word, but can you blame him? Having to spend so much time around Jim and Spock is obviously getting to Bones. Those two really should get a room.
This is not a slip up. McCoy was completely correct. Bisexual is another word for hermaphrodite. In other words they have both male and female organs. So there is no way this could be asexual reproduction. Now that is college biology.