No, it has to do with every time you move the mouse over a window, a hover event is sent to the application, which runs its main event loop. Either the installer only updated its progress bar when an event happened (in which case it would only appear to be going faster, because the progress bar would move more smoothly) or there was some really terribly written code that literally only made progress when an (unrelated) event happened. My guess is the former.

Being a bored kid in the 90s with nothing better to do, I had timed it. It was actually faster.