I'd guess the legal difference could be between taking something you have no right to (theft) and keeping hold of something you had a right to but should have g

I'd guess the legal difference could be between taking something you have no right to (theft) and keeping hold of something you had a right to but should have given back (he could argue he forgot, or hadn't yet sent it back). But from a cultural point of view it's obviously completely different. Anyone sane who let an employee go and realised he hadn't given back his laptop would tell them to give it back, not scream for jail team.