A person who takes money to learn and goofs off is just as much a robber as an employee who goofs off.
Pay checks are for working, so if he goofs off, he’s a gazlan.
Kollel checks are s’char battalah, so it’s not gezeilah to goof off – he’s batteling!
Gavra’s right though that it’s bad for everyone else. It’s obviously wrong either way, but probably not technically gezel.