Question about country of origin

I've been seeing comments saying that Tintin is not actually going to be Public Domain in the U.S. in 2025 due to it not being Public Domain in Belgium which is it's country of origin and the U.S. being a signatory on the Berne Convention means that it's not eligible for Public Domain in the U.S. as long as it's not Public Domain in its country of origin. Is this in fact the case? As I've understood it, the Berne Convention sets up a minimum standard of copyright protection within signatory countries, but each country still has its own specific laws that may vary regardless of country of origin, but I could be wrong.
This would however, from my understanding, mean that Winnie-the-Pooh would still be under copyright in the U.S. until 2026 due to his country of origin, England, carrying the copyright law of 70+ life.