mistake

I usually contact users when I see they are online on steam, just so they know they won something.
Not like I was agressive lol

The way you worded your initial comment ("You didn't apply key mate") only makes sense if the giveaway creator was online on Steamgifts, but even then, yeah, it does come across as accusatory and impatient (and perhaps a bit aggressive), actually. That said, I agree the giveaway creator took things way overboard.

P.S. I think "calling out" is against the rules.