the logic is simple, it dropped because of rng. that legendary engram could easly have been green or blue, but i got a lucky roll and got a purple. if there was a loot system that based drops of level of mobs or things like that then it might be different, but since you can get the same engram drops from a level 6 mob as a level 26 mob, it's not really earning it from rng. if you go to work and get a pay check and buy an item from the store you would say you earned that item through hard work, but if you found that money on the street and bought an item, then you just got lucky. that is the difference between getting an rng drop and buying stuff from Xur