The majority of visible trees (bar the Melaleuca he mentions) are Acacia and Eucalypt, the 2 fastest growing trees in Australia. Not to mention the La Nina. I did read a study once where it was theorised that Eucs aren’t pioneers, they are hyperpioneers. Hyper meaning “wow, that’s fast” in scientific terms.
In regards to grass competition, what he has done there wouldn’t fly in the Aus sub/tropics, exotic grass and vine growth would have pulled most of them down. But in relation to what he is illustrating with 24 hours of work and then hands off forever, it’s certainly demonstrating how easy it is to make a tangible difference.