Destiny engrams don't always work out the way you expected
Destiny players: engrams may decrypt as class-specific items inappropriate to your character. Even when you buy them from the Cryptarch.
Destiny veterans are probably already aware of this but it's worth a PSA anyway: you don't want to spend all your rare currency on engrams. It's much safer to buy gear from the Vanguards, Crucible vendors or Xur.
The video by WeepingHoney above is a heart wrenching reminder of this valuable lesson - and a call to Bungie to do something about its occasionally frustrating loot system. Even if events like this are endlessly amusing to everyone else.