An article from KellyB isn’t the most convincing thing in the world. Again, he is running submax in the video in both effort and speed, which is why he runs much different in the sled video (he can’t run submax if he has to pull a heavy tire like that).
I’ve seen dozens of videos of Silencer’s running. I understand what is going on. I can also say there is no such thing as “quad” running. In the video with the sled, where he is running maximally, and in his race videos, he is clearly getting hip extension and using his glutes and hamstrings. If anything should have been noted from his submax video, it should have been primarily his excessive curving of the neck and upper back, which will put a large strain and stretch on the hamstrings (and put his pelvis out of position) and likely lead to a hamstring or adductor strain if he started to push it.