So you have to count the EU as a single country to push China into third place. This is something people argue about. During Brexit I many people assured me the EU was not a country.

If you use PPP rather than nominal GDP China is actually the biggest and the EU the third biggest.

Also worth noting that, despite expansion, the EU was a smaller proportion of the worth economy before the UK left, than the EEC was after Britain joined. The trend is very much away from the West.