The point is not about literal forests, it's about the fact that just because there is 10m between people doesn't mean that you can therefore tile the world wit

The point is not about literal forests, it's about the fact that just because there is 10m between people doesn't mean that you can therefore tile the world with humans 10m apart (or even closer). You need empty space, huge amounts of it, to make life not horrific. Whether that space is forests or ocean isn't the important aspect. What's important is that just because there is 'empty' space doesn't mean that filling it with more people won't have an impact on how people live.