What does it mean if my cat's puke smells like poop?

My cat, Barnacle, puked everywhere this morning, I have no idea why, but it smelled like absolute shit. Literally, shit. Like diahrrea. But I saw him do it and am 99.9% positive that it came out of his mouth. It looked like he was hacking up a hairball except it was just a ton of vomit coming out. When we cleaned the mess up about an hour later we re entered the room and again, it smelled like there was a vat of shit in there. Is that a bad thing? Has your cat ever done this before? It’s weird.