I get the impression that this guy is primarily out to sell his book, which he spends quite a bit of time talking about how great it is. As for the points he mentions, some are clearly false.

> The amount of land we use for meat — humankind’s biggest use of land — has declined by an area nearly as large as Alaska

With global population trends, even if average meat consumption is starting to decrease, the amount of livestock raised will still increase. I actually found it difficult to find a good measurement, but this site seemed to be credible https://ourworldindata.org/land-use

> Fires have declined 25% around the world since 2003

This seems to be untrue, at least in the US - https://www.epa.gov/climate-indicators/climate-change-indica...

> Habitat loss and the direct killing of wild animals are bigger threats to species than climate change

> Humans are not causing a “sixth mass extinction”

Which is it? Are we not causing any issues, or are we destroying native habitats?

In the end, I don't really know who this guy is, but for all the fundraising he did as a teenager, I don't think he's doing environmentalists any favors anymore.