Your skepticism is unwarranted - it's real. There's a documentary about it. Small droplets of rotting fat float up to the surface, where the dog can smell it. They had to account for ocean currents and the rate at which the bubbles rise in order to sufficiently narrow the search area. They couldn't find it at first, because they misunderstood the mechanism and assumed it was gas bubbles, which obviously rise at a different rate.

Besides - where else would they have gotten the information from? She was killed on a submarine with no one else aboard but her murderer, and he wasn't talking.

They've been using dogs to test COVID samples, and discovered they're more accurate than the chemical tests.

My beagle once lead me through a park about 80 feet to a dropped slice of pizza.

So, yeah, given a body is going to be a massive horrible smell that's a lot easier to find than cold pizza, this is entirely plausible.

Dogs smell in stereo with detailed temporal information. They know which way a deer passed and how many days ago.