Please consider national security. And the international situation. There's something to be gained in the appearances of being of one mind as a country and much to be gained by those who would harm us by the appearances of disorder and contradictions among President and former Presidents.
I do not excuse nor consider to be even remotely acceptable or excusable the behavior of Bill Clinton, from the look of things, throughout most of his life. But I CAN see how President Bush could be publicly courteous about him if only for the reason the man served as President of the U.S.A. It's worth a degree of respect, for that reason alone, and probably that's the degree of respect President Bush was describing.
About Hillary, I just think he was being smart, at least smarter than she is with her shrill nastiness about nearly anyone not in her control.