(edited by CharlieGR.4307)
Achievement bug?
Acheivements are account-wide, this includes deleted characters. (IE: I have a character who had 41% Tyria Map completion, but deleted that character, the acheivement still knows that character had that amount.) I had minions on deleted characters before the whole account-wide minion system as well, so I lucked out and never will get my digital deluxe minion again either.
It could be that you forgot you did them, or like you said, it was awarded by purchasing something, doing an event you forgot about, etc.
Sometimes, there are bugs (giving credit when the item has not been acquired) in collections (it is somewhat common), or…it may be from the armor found in your Heroic Chest.
I would not worry about it much.
Welcome to Tyria, and happy adventuring!
The old hint completion achievement is actually obsolete as they had replaced it some time ago, perhaps they automatically give credit for it now?
And a possible explanation for having that helm skin is if you chose to start with a helm on your character creation, I know some classes allow for that.
Wardrobe is account wide and never locked.
I’m assuming you’re a warrior? I think if you pick the helmet as your starting armour, it has the same skin/appearance as one of the crafted helmets for that collection.