There's nothing in particular about the jellyfish that's taken a shine to Wash that makes it stand out from the others, except for the fact that it's on the larger side. On the rightmost slope of the bell curve, one might say. (This is a jellyfish pun.) That being said, it will absolutely approach Wash in the future if he reenters the caverns. Like, immediately. It will bumrush him like a golden retriever greeting its owner at the door.

Even as he moves to leave, it seems kind of reluctant to let him go. Bobbing after him, it flashes the question mark again a couple of times. Hey, come to think of it, that's pretty distinctive, isn't it.