#1 - It's Olivier Busquet, not Oliver, and there's only one of him playing so no "s" at the end of his name.
#2 - Busquet could easily sense shenanigins on Mueller's limp and figured him to be stronger than his limp would indicate. Maybe - easy to say now, BUT... The flop comes and again Busquet correctly deduces it is just a C-bet from Mueller (a pretty strong one at that that screams go away) and he has not hit that flop - so let's find out by coming over the top. After all, Busquet knows that Mueller knows that he literally can have any two cards since he did not have to commit more than his BB to see the flop. Mueller would have to have a 9 to crush him - making Busquet odds
on favorite to have best hand. Time to bet it hard and not allow room for a suck out. Is it second nature for you to know that the odds of Mueller hitting that flop is only about 30%? It is for these guys.
#3 - You do not say what their stacks are (VERY IMPORTANT INFO)- but I find people get genuinely confused by pro play because they fail to take that into account. Look at the crazy plays at WSOP
or WPT final tables you see. Why did they do it? Hell, why not? They are usually sitting at a "massive" number of big blinds and can afford to shift to a LAGtard gear and spin the wheel of fortune. The worst they figure can happen is lose 2% of their stack AND cultivate an image that induces action from the other players down the road.