Alleged by the opposite side that is. There is no proof of that.
>although it's less plausible since the separatists are not operating any air assets that I'm aware of
Ukrainians have recently accused Russians of downing their SU-25 by air-to-air missile fired from a Russian jet Moreover, Ukrainians have a history of mistakenly downing a passenger jet (in 2001, russian jet comming from Israel), although so do Russians (Korean Boing), Americans (Iranian Boing), Israelis and some others.
I guess that's what they were saying about Union soldiers too
They are trying to "Terrorize" the Ukrainian government into giving them sovereignty.
Obviously, these rebels are freedom-fighters, not terrorists. Even you felt that you needed to put "terrorize" into quotes.
This isn't even particularly sneakily implemented; for anyone with slightest amount of understanding on cryptography it's obvious that this is the case.