Not going low enough. A pullup requires you to straighten your arms completely to 180 degrees. He's not even getting to 90 degrees. It's not anything resembling a real pullup.

It was the one challenge video I clicked through because it seemed like the most difficult. 40 pullups is a hard task.

I wish Max wouldn't lie to market himself.

When doing proper pull-ups you have to hang while keeping your back muscles engaged and with hands wider than your shoulders; pulling yourself up from that position is challenging. https://www.youtube.com/watch?v=oYpSV-_gBaE

I'll disagree slightly with posters who say that your arms should be straight 180 degrees at the bottom of the movement, since you want to keep your shoulders engaged throughout; a slight bend through the elbow is best, I think.

But by slight I mean 170 degrees or something, not 80 or whatever this guy is doing.

Bottom - arms straight. Top - chin above the bar.

Anything less than that is not a pull-up.