It's a good video. He based his work on / followed the protocol described in the Nature paper published by the lab mentioned in the article (https://www.nature.com/articles/nature25476).
I've seen this video, he did a pretty good job, but his chemical treatment didn't penetrate at all. I suspect he would have benefitted from pressure cooker during that step. this is how treated lumber is treated to get full penetration of whatever chemicals they use.
given the depth the of the penetration, he basically case hardened it. you can see in the bullet tests that the interior laminations are much fatter than the exterior layers.