I just bought two exotic armor engrams from Xur and both were Crest of Alpha Lupi for the Titan, my friend bought one and he got the same thing, how is that possible? Shouldn't the Exotic engrams drop different items?
Exotic engrams can decode into an item you already have. They can also decode into the same item twice in a row. This is the RNG aspect of Destiny. Exotic engrams can drop different items, but you were just unlucky and got the same item twice.