To note, he did that on the track. I know theoretically and practically it is faster to do it that way (his track records are better than his road records). Still, the idea of doing 754 laps on an outdoor track over a 24-hour period (31 laps an hour) is insane.
If it makes you feel better, in his first year of ultrarunning he ran 177 miles in 24 hours at Flushing Meadows Corona Park in Queens, NYC. The next year during Hurricane Gloria (1985) he broke that record by a mile - weather that in today's day and age many races would be cancelled, and in a year where many runners retired early. Yes, he ran his 303km on a track so everything he needed was readily available and there were no tangents to worry about.
Once you go the "but that's insane" route, you've lost the argument. Everyone has some distance, terrain, conditions that aren't reasonable -that's fine - no one is making you run it. But if you want to be able to discuss it objectively in the difficulty of the achievement, you need to make a better argument than that. This coming weekend will see a heard of strong 24 hour runners hit the track in Philadelphia. You are welcome to go watch and see if anyone comes within 31 miles (yes, a full 50K) of Kouros.