Its correct he failed to do the task because take out Ironhide with a stealth attack means he needed to get invisible and goes behind Ironhide then you can press square and sharpshot does a stealth takedown (he place C4 on his back and then it makes boom)it also one shot Ironhide when he is Full health
Man this mission its very good and yeah there is a 85% that Sharpshot could kick Ironhide in the nuts and then put a detpack on his back to defeat him, after cloaking.
There is a Super-Duper-HYPER-MEGA-EASY way to defeat Ironhide, you just Cloak, and attck him from behind; Sharphot will kick him in the "balls", and put a deckpack on his back. The explosion defeats him instantly.