Looking back, you're right it doesn't really fit in with the show. And straightening his tie, seemed like they wanted to give him a grand send off. As I was sat watching the scene unfold, for a split second, the writers wanted to think that Gus is invincible. At the time it was quite dramatic for me anyway
In a previous episode there was a vigorous pat down of Jesse by that bulky bodyguard, and he appeared to take something from him. It had already been established that Saul had been in contact with the mother at least once, and it was probably in his own best interest that Gus was out of the picture.
Biggest thing for me is that when his family is involved (and in danger), Walt really doesn't seem to have any limits.