Anybody here do weird achievements?

So quick question; several times now I have gotten achievements without doing the rquired stipulations. One example is in campaign you are supposed to perform an assassination against an elite to survive a fall that would have been fatal, I got this achievement on Sword Base in Co-op, I was running up to help a teammate and an elite got in front of me with its back to me so I assassinated it and got the achievement all the while I was being shot by the ultra with a concussion rifle. I also I have the cracking skulls without have the defiant map pack as well as REturn to Sender and Poppin and Locking Candy from a Baby Offensive Driver Totally Worth it and You ate all the Chips. I have no Noble Map packs nor the defiant map packs yet I still got the achievements.