He's dead kiddo move along

In the episode where the CMC are finding a date for Cheerilee, the song has a line where Sweetie Belle jumps on the back of an old pony at a funeral and sings "this one's too old!".

Yeah that I know, of course. But I don't get why it relates to lion king.

It's like the Spongebob "Up next" meme.
It is supposedly funny because the post is showing Simba mourning his dad's death (which is emotional) and Sweetie Belle hijacks the scene, happily singing.