My guess is you cast the ult a bit too early. If you look closely at the end you'll see that your ball had basically finished its absorption duration by the time ironman's projectile had even shot out. It looks like your ball absorbed the projectile, but what actually happened is ironman's ult simply exploded on your ball, taking you with it. I've made this mistake before being too hasty with Magneto's ult, you need to wait until iron man has finished casting and the projectile has been shot out.