Seeing as how there is a literal 0% chance of someone with no training experience "repping" 465, here's my theory:

Dude is an amateur powerlifter, which explains the DYEL look despite strength.

New to gym, wants to boost his ego a bit. Sees someone working with a weight he knows he can pull. Tries the whole "gee mister what is blobbybalding??" canard to make you think he's weak. Meanwhile his whole plan is to go in for the kill and rep what you're working with to leave you surprised, but you won't let him. Finally finds his chance when you literally leave your station, cue you returning to find him lifting your weights.

His ego is boosted because he got it off the ground, you're left confused and worried about his bad form. Nobody won. End of story.