I did an ultra in the Alps this year. About 8 hours into my race, my legs were just giving out. I was only about half-way done (time-wise). It was humbling. Sort of like the feeling you get after doing as many pushups as you can... you just can't do "a few more" at some point.
The gun went off at 1am and the lead guys (not me) were running sub-6 pace through town. Then they hit a narrow staircase leading out of town up into the Alps. They hammered those stairs and hit the switchbacks, still running hard. But at every aid-station there is a ton of lost time just eating, refilling water, and changing into dry shoes/clothes (it rained for the first 6.5 hours of my race).
It is similar to someone saying, "are the guys who climb Mt. Everest just walking up to the top?" Yes, one some level, they are. But is that really the best way to describe it? Which is harder? Benching 400lbs once or doing 200 pushups without stopping? It is literally the same motion and the same muscle groups. So which one do you think you could do?
Racing ultras is different than racing the 1500m on the track, but you aren't "walking."