i am confused,

The Gaster is Undyne thing was a joke, this one is an unrelated joke

Gaster being Undyne was a joke. However the Paintedfish thing is very much real. Long story short fish simps for other fish, they are now fanonly canon

Welp. Gaster being Undyne is hypothetical, which means it’s not 100 certain. Plus ik what Undyne is like ;)