It comes as a shock, I know very well. Some 4-5 years ago Trez scored such a goal and I argued that it wasn't offside. But in the end, I learned that it was, and Trez himself said that it's offside. It's just that 99.9% of the offsides are called because there is only one player in front of the attacker (the goalkeeper) and there needs to be two players. With time, we simply forgot to count the goalkeeper