This appears to be depressingly common
And by depressingly common i mean more than one teacher does it
which is more than one teacher too many
If you got 100% of the answers correct and nothing's perfect then that means 100% isn't perfect
which means he isn't proving anything by not giving you a 100% score.
And even if he is, it's stupid and he should still give you a 100% score because that's the only one that makes sense
mathematical sense
you'd think he'd get this, he's a maths teacher.
And even otherwise, you got 100% and not giving you 100% for it is annoying and stupid.