Himaruya hasn’t actually confirmed that he based Estonia on himself. Fans have speculated this because in the few instances where he draws himself, he looks like Estonia.
Yes, there are some nations which he based on people he met, sometimes unintentionally too.
America was based on a Canadian he met. He had a friend from Ecuador that he probably based the respective country on. He also joked that the more he drew Thailand, the more it became obvious that it looked exactly like his Thai friend.
Ellawritesficssometimes 