That's just the contestants being weird. I mean, it's not the only episode that they used first and last names.
True. I remember this from The Golden Cricket Cage of Khan.
Kirk: And on the Silver Snakes, we have?
Tia: Tia Thomas, and I'm 11 years old.
Kirk: And?
Jon: Jon, I'm 13.
Kirk: Let's hear it for the Silver Snakes!
And in Ponce de Leon and the Lost Fountain of Youth, the girl on the Green Monkeys was Jessica Hill. I didn't catch her partner's name thou. (And I've seen the episode three times, too!)