Was his assessment basically just playing video games? I've noticed that's an activity I can do proficiently for an extended duration on very little sleep (along with things like "bulk" coding) but there are others I'm awful at unless I'm well rested (eg. complex planning, creative efforts like songwriting) and I've found my communication skills start to become impaired when I'm really sleep deprived. I'd be curious…
I'm actually refactoring some of the code/sub systems I created during that time now and some solutions are very wacky...creative, but a super weird way to approach it.
Sleep deprivation might not have been the only contributor, but there a noticeable change in our code base during that time and I distinctly remember worrying about my sleep