Scat—because the elf maid is inside the giantess's ms Mauseru large intestine. The elf maid—hears something approaching her: it is the giantess's elf ms Mauseru's poop.

I think the right term for this description would be "corpophilia" which I think I remember being on the site, but can't find any evidence of this.

It should just say "Content that revolves around excrement"

"Usually" is the key word here which means most but not all. But your description is lacking that part, because as it is, it essentially says that a work is only Scat when Sexual Arousal is involved, when even the definition of scat refers to the excrement itself.

Yes. But usually scat is used in a sexual way.

Not exactly an accurate description, there are plenty of scat works like Shiina Nami's that revolve around characters going about their daily lives and just excreting on toilets with relief, but not necessarily sexually aroused.