The way he is restraining the mantis with the thorax and legs out is technically how you would restrain a mantis if you wanted to hold it still for some reason. Mostly his handling however just speaks of lack of experience. He looks like he is afraid the mantises are going to bolt/fly so he keeps trying to semi hold them, which just results in them trying to rip free anytime their legs come in contact with something they can grab. He gets bitten for the manhandling in the first video, but if you notice he does not swat or react instead simply releasing his hold and lets the mantis relax on its own. Obviously with that kind of reaction at a bite he is not purposely being "mean." The mantises aren't getting hurt the way he is handling them, it is just making things harder than it has to be, which he seems to realize as he switches to a more relax let them crawl on me versus try to hold onto them stance.