Assuming the sheep are only fed from the grass they eat on-site, how are they NOT carbon neutral?

You’re correct that they take in the same number of carbon atoms as they eventually exhale/excrete/etc… So, in that sense, they are carbon-neutral.

But that doesn’t mean they’re climate-neutral, because when you combine carbon atoms with 4x hydrogen, you get methane, which for physical reasons has a significantly stronger greenhouse effect than CO2. And ruminants (like sheep and cows) belch out lots of methane: https://en.wikipedia.org/wiki/Ruminant#Ruminants_and_climate_change

I wondered if you were going to go the methane angle. Like most of the points here, you're not wrong, but focusing on it negates the overall good.

That’s why even people who would immediately choke to death, if they ate a vegetable, could still help out on the climate front, if they switched from beef (and mutton) to poultry and pork. See this graph, for example: https://ourworldindata.org/explorers/food-footprints

But every conversation has to be injected with this message?

And yeah, reading through the article, I’m happy that it’s being used for solar, I’m happy that if we’re already raising sheep, they’re at least being used relatively efficiently, I’m even happy that the sheep are living a relatively happy life.

What I’m less happy about, is that OP vegan was pretty spot on. They’re raising additional sheep for this endeavour. And no one had the expert knowledge to ask, if the belching sheep maybe somewhat undermine the climate advantages of solar.

Because that wasn't the choices. It was mow with fossil fuels or mow with sheep. This is what becomes so tiresome about the vegan injection. Yes things can be better. Yes this isn't perfect. No, veganism isn't the only way to achieve improved results.