Was Mace Windu apologetic to Ahsoka Tano? When she is invited to rejoin the Jedi Order, he says to her; "this was actually your great trial, now we see that. We understand that the Force works in mysterious ways, and because of this trial, you have become a greater Jedi than you would have otherwise". Doesn't sound like an apology does it? So was it a praise, an observation, or a subtle attempt to deflect blame of his mistake onto the Force?
No, he is not being apologetic. Lets take a look at his quote in context.
Ki-Adi-Mundi: This is the true sign of a Jedi Knight.
Mace Windu: This was actually your great trial. Now we see that. We understand that the Force works in mysterious ways, and because of this trial, you have become a greater Jedi than you would have otherwise.
Yoda: Back into the Order you may come.
Star Wars: The Clone Wars - The Wrong Jedi
The subtext is that they were wrong to kick her out of the Order, and they make this right by letting her back in. However, the Council considered her ordeal in hindsight as being her Trials and, having proven herself ready and worthy, offered her the promotion to Jedi Knight. They are not apologizing, or offering the position out of some sense of guilt, or even blaming the Force. They are simply acknowledging something happened, and that as a result, Ahsoka is a worthy of being a Jedi Knight.
Going by his wording, and given what we understand about the Star Wars universe, Mace's words may not have been an attempt to deflect blame, but rather an accurate assessment of the situation.
The Force does have a will of it's own, and it does work in mysterious ways. For example, we can say that Anakin was indeed the one that brought balance to the Force, despite the fact that he spent so many years working for Palpatine. The Force does not directly arrange events to quickly come to the conclusion that it's will demands, but rather guides people through experiences (some good and some bad). In short, there appears to be an allegory being drawn between the Force and the Judaeo-Christian God (the most blatant example of this being "the Force works in mysterious ways"). The biggest difference between these two concepts is that, in the Star Wars universe, the existence of the Force is not as fiercely debated.
With that in mind, consider the fact that both Mace and Ahsoka have dedicated their lives to the service of the will of the Force. They understand that the events in their lives are guided by the Force, and that sometimes even their actions are guided by the Force (consider Luke's blindfold lightsaber training). So when Mace says that this was Ahsoka's great trial, he may not be attempting to deflect blame. He may very well be sincerely congratulating Ahsoka for passing the trial that the Force had given her.