Being labelled as a day trader or not most likely did not have anything to do with that margin call - they're normally issued when one or more of your leveraged trades tank and you don't have enough money in the account to cover the shortfall.
I trade quite often, but not as much to be labelled as a day trader based on what I read, but I'd still like to know what would be the consequences for me if I were labelled a day trader.