Shouldn't this game be part of the Yoshi series?

Technically, no because its part of the Super Mario Advance Series, and I don't think a game can belong to more than one category

it's changed, it's now belonging to both of them...

Series Mods cannot remove games from the series, if this seriously bothers you to the point where you make 2 threads about it in the same week, plead your case to an admin.