The France U21 midfielder had a year's loan at St Andrew's.
Boga told Foot Mercato: "The goal has been achieved, we managed to save ourselves. We had ups and downs. I only remember the positive. I still managed to play 32-34 games, so I'm happy.
"It is certain that I progressed, in the mental and physical aspect in particular because it was complicated. We played a long time down the table and we had to be strong mentally, and suddenly it allowed me to progress. There is a lot of intensity in the Championship, you can beat everyone, it's a very open championship.
"Compared to Ligue 1, it's much more physical, stronger in intensity."