Yes, it's poorly done. You can just pause Youtube and take it in, though. Anyway, most of the interstitial text won't mean a lot if you're not familiar with the text they're referencing.
You say "but" as that shadows their achievement somehow. You don't even need to go to the Amiga; it points out right in the intro that the C64 (released only a year after the IBM 5150, and vastly cheaper) could outperform the 5150 in almost every way. The point is that they accomplished something that should have been impossible on that hardware.