While I don't know if this is cruel or not (and don't feel invested in making an informed opinion), what the person said does not mean that it's not cruelty.

Let's break this down logically.

Assertion: "animal cruelty is not funny"

Assertion 2: "neither is being a killjoy"

When neither is used in this manner, it means "true, but also". Thereby, assertion two is essentially piggybacking onto assertion one in the following manner:

"Animal cruelty is not funny, but also, being a killjoy is not funny"

I hope this explanation helped, and yes, I'm fun at parties, but I prefer to avoid loud ones where beer and drugs are involved. I'm more of a lan party type of guy.