Well, yeah, it's obvious what is meant
by the scene. But I wonder if anyone really would have thought he was the same, earlier, Benzite? It certainly never occurred to me since if it was
it'd be a plot point in the episode and that'd make no sense; since there's no way Mordock would be a serving officer now and we were just told
Mendon was part of alien exchange program.
It would've been better to do the scene with Wesley saying, "Hey! My friend Mordock is a Benzite!"
"Yes, Mordock. The first Benzite in your Starfleet. There's much praise for him back on our homeworld."
Explains to the audience what's going on (yeah, this is the same actor, but it's not the same guy Wesley met earlier) and doesn't make Wesley a clueless ass who just sees a blue catfish-alien and automatically assumes it to be a guy he met a year earlier.
The "Racist" comment, again, is tongue-in-cheek as obviously what's going on is trying to explain things to the audience, Benzites just might have some aspect of their genes that does allow for "identical twins" to occur in the general population without there being and genetic relationship between the individuals. But the way it comes across on first blush just sounds odd.