Sheep farmer here. You are right to be suspicious.

Healthy sheep poo does indeed look like a little pile of loose pebbles. However it is not uncommon for something to cause their stool to turn into a lump or patty. The pebbles can cluster together like pomegranate seeds or dissolve into a single mass of varying viscosity. The cause can be everything from diet changes, bacterial infections, parasitic infestations, or even stress.

If I owned the sheep that produced the sample from Wikimedia, I would be concerned about the animal’s health and be looking to intervene actively. That turd just ain’t right.