They're just having a laugh. Just like when our floorboards creak upstairs when we're all sat in front of the TV and we joke about our own little visitors!The little conversation at 5:14 between the two astronauts is pretty damn interesting, they've had visitors again, even for the die-hard 'logical' people this must ring certain alarm bells.
All you hear is that piece of dialogue with no idea of the context it's being used in. And they probably are just having a bit of a laugh. Probably gets a bit boring on the moon
