While the episodes are part of Season 2 outside of Japan, the second season is technically a sequel series called "THE ビッグオー second season" so the following anime rule applies:

Sequels series (i.e. a direct continuation of the story) are added within the same entry. When the episodes numbers are continuous, all episodes are added to the same season. When the episode count is restarted (i.e. the first episode is Episode 1), the new episodes are added as a new season.

As you can see here and here, the episode numbers (called Acts) are continuous. There is an episode group for that splits the series into two seasons available here.

P.S. I know it has "second season" in the title but Japan doesn't really use "seasons" the way the rest of the world does; anime typically are split into cours. You can learn more about our anime guidelins here - https://www.themoviedb.org/bible/tv/59f743289251416e71000037#5b71c6b4c3a3684161000001