IPv4 Games

I operate an online service at https://ipv4.games/ that invites people to send http requests to my web server from a lot of different IP addresses. In order to claim an IP, you need to successfully make a tcp three-way handshake with a VM on Google's network. Somehow a player in Europe named femboy.cat has successfully managed to claim 20 million IPs, which is 9% of all IPv4 hosts according to Censys. Does anyone have any idea how they're doing it? Would anyone here be willing to be their North American rival?