I'm...suspicious. 10 months ago this account was whinging about the evils of AI and this is heavily AI driven code. README claims to be a Norwegian developed browser but account is in Qatar. Andreas Røsdal has two github accounts, both andreasrosdal and andreasrosdalw, one of which has forked a project from the other or I would just think "oh two people with the same name".
Having the prebuilt client and art assets you hack and change on saves you million of up front cost.
The foldingideas videos about decentraland talks about this. "Dead" mmorpgs work on a small skeleton crew despite the original game having taken 100s of people years to make. Looking it up the turtle wow server was like 5-10k concurrent players? A lot for sure but bordering on that category.
It takes a lot of work to manage that but nothing compared to making an original IP from scratch.