Got Honor lvl 3 message, then 10 minutes later I got banned.

Ya because honor level protects you from getting banned.

i mean, lv 3 honor is pretty low, most casual players are now at 4 and 5 since its implementation. You mostly just grind out games, honor and if everyone honors then you get a exp on your honor level, case being that you really don't get honor levels by being a good player like 1-5 mastery ranks, you just have to do it enough.

yes. if you're toxic you can get banned no matter what your honor level is