Is this weird?

[Scilfulled]

Boss kept telling me to go home as I didn't have much to do but I felt bad being first one to leave! Then about twenty minutes later, he was like seriously just go home (he knew I wasn't doing a lot and have work exams to prepare for) - should I just have gone immediately the first time? I never know the etiquette with these things

totally depends on the company you work for.

If it's a small business with a few employees and everyone's nice and your boss KNOWS this is a lean time and you have exams then it's fine.

Your boss may expect you to return the favour at a later date when you don't have exams and they're busier and not expect to pay you overtime.

Or, if it's some major corporate, maybe it's a ruse to sack you for being lazy.

Quite hard to tell from your post.

It's a major corporate but he meant it and was being nice! No overtime and I will be expected to work crazy hours at other times to compensate.

Yes you should have just gone the first time