According to the developers on discord, the guy with the level 1000 tank (not just level 100! Far as my eyes can tell, at least) was a cheater who's been banned. Apparently the cheat required a rather in-depth knowledge of programming skill or something.

The 2nd place person is legit though (a very active participant on discord)

As an aside, that week long headstart that certain countries got is such BS when it comes to ranking systems-_-