It does count toward the final score, as does searching all of level 5 even if you beat Goo and find the Rat King. If you don’t search the entire level you lose points.
The wiki says that for the exploration score you only need to reveal all hidden doors, items, open all containers (except crystal chests), solve all puzzle rooms, complete sacrifice rooms, etc. You don’t need to explore boss rooms fully afaik.
It does count toward the final score, as does searching all of level 5 even if you beat Goo and find the Rat King. If you don’t search the entire level you lose points.
The wiki says that for the exploration score you only need to reveal all hidden doors, items, open all containers (except crystal chests), solve all puzzle rooms, complete sacrifice rooms, etc. You don’t need to explore boss rooms fully afaik.