“There has been no photo evidence of the pro-Russian protestors having any AA capability, at all.”
“I imagine Russian Spetznaz would have SA-18’s.”
If they had SA-18’s, there would be four jets down, not one. In the vids, they are flying too low and slow not to get hit by them.
I’d lean to mechanical failure, or local ground fire. They were flying REALLY low. That is a lesson they will have to learn about the hard way, I guess.
I expect they were instructed to scare the rebels. If ground fire brought an aircraft down, they'll probably send ground troops to take the airport rather than risk bombing it into rubble.