That Popp would be shocked at Mithrun's past is no surprise; even if he isn't from Mithrun's world, wouldn't know as much as even the most uninformed party about the implications of Mithrun's past as a dungeon lord, he has no doubt gathered enough from what he has seen.

...Mithrun, of course, is not privy to how much more Popp extrapolates from there, but that is another issue entirely. In fact, the conclusions Popp actually voices seem perfectly reasonable to him, even if not perfectly accurate. "Not really a matter of determination... but, yes."