Why did this tube imploded four-fold?

I was watching a video from an implosion of a pipe under pressure. You can see it was squeezed together.

However my question is, if the pressure was uniform, why there are four folds? The tube was circular.

Initially I thought, well easy... from bottom, top, left and right. But that's a human invention, with the sides. Nature doesn't care what labels we give to each direction. I don't think there's anything intrisicly four-related here is it?

Why didn't it fold into 2-fold, 3-fold or 5-fold for that matter?