He wasn't, he was just a very promising player. His first season at Dortmund was OK but not special apart from his young age. He only scored 4 goals.
He was chosen for England at 17 but didn't score an international goal in first 10 games. He was 19 when he finally scored which for a number 10 that isn't great.
All for the hype behind Rigg but comparing rigg and bellingham and the championship to the bundesliga is wild like.