Your update is not clear - were you in the game when someone else killed last Uber and you just picked it up OR you just picked up when someone killed three days ago and just dropped it in your game for you?
Timeline:
I got a standard of heroes yesterday. RockyIsBack was not in the game (I don't know them)
Today I dropped that same standard of heroes on the a1 ground. RockyIsBack picked it up.
They report they got the Steam "it has a purpose" achievement
So no--it does NOT appear to work like the chronicle where you need to be in-game at the time of drop. Just having any old standard should pop the Steam achievement.