"Slippery slopes" happen when one action or policy ends up having wider or larger consequences than intended, nuance gets thrown out the window, and things that are different end up getting treated the same. One favorite example is, of course, that allowing gay marriage will lead to people marrying their pets. Or in this case, that a ban on videos portraying violence against feminist video game characters will lead to a ban on all violent video game videos, regardless of any differentiating context.
But both the OP and you are clearly stating the opposite - that two videos will be treated
differently because one lacks a characteristic the other has.
It seems to me that what you and the OP are actually bothered by is a sense that it's hypocritical to ban this video, but not other similarly violent videos*, and you're responding by throwing out a term that's often used by anti-PC types. It just doesn't apply here, though. Slippery slopes don't exist on well-defined surfaces.
*
And as @Tornado just pointed out, this hypocrisy is hypothetical, and likely would turn out to not exist in practice