More like it would take the jungles 3 weeks to wipe out 7 billion people. Act like most people can survive in the wilderness brehs.
You kidding? Most of those people would die. Fuck, I would, probably by my own hand. Fuck the outdoors 
It's about numbers. Based on the dude's nondescript concept of people "returning to the jungle" or "natural state", I'd say the game parameters are...
All human beings must move to and live in tropical or subtropical rainforest biomes.
No cities, no factories and no agriculture allowed.
No oil, no gas, no coal. No generators or vehicles that rely upon any of those are allowed.
Guns, hand tools and canned foods from current civilization are ok but only what can be carried and you can't return to cities to retrieve more once you've left.
Billions of people tightly confined and
simply existing for a short period of time- slashing, burning, consuming and turning the rivers into shit would be enough to obliterate the forested areas in short order. Diseases couldn't kill the people fast enough to save the local ecosystem from the human scourge. And even with massive human casualties from disease and starvation in the first few months (including heavy violence and probably a lot of cannibalism), the local environments would be stripped bare with the people eventually destroying themselves as resources run out. The jungle isn't "winning" that scenario, and neither are the humans.
I mean, the mosquitoes will be happy at least.