Some highly uninformed opinons here:
OK first up it isn't a singlular sad 'guy'; QDQ is a long-term project (read: over 10 years, long before these new-fangled games like "Quake 3") involving many people. QDQ runs are typically the best-of-the-best, demos from multiple players spliced together (as different players are better at different levels).
Secondly, the level 9mins in is E1M7. Anyone who has played through Quake, heck, even the shareware version, knows that that on that level there is only one enemy you directly kill (via electric shock), the boss Chton. Once you kill him, a bunch of other enemies get automatically gibbed by the game (and that's the only way to kill them as they don't 'appear' until then. If you look, you can see (and hear) them getting gibbed at the intermission screen.
Come on then doubters, quote video times on all these other alleged 'non-kills', I'm still waiting.