You should play the game that you saw it being done, then. Destiny does not have player trading in any form, so having seen it done with your friends is either your mind playing tricks on you, your friends playing tricks on you, or you were playing a different game. The only time another player 'gives' something to people are the reputation boosters, as the buff is added to all fireteam members; the item isn't given to anyone, the person who has it uses it, and the buff is shared.