Seems the most likely, for all the usual reasons, and it seems pretty clear from recent conflicts that Russia still subscribes to the game plan of mass numbers of expendable troops, equipment, etc less so well trained.
Probably little choice when you're running a Kleptocracy. It appears there's no part of the Russian system immune to corruption / etc.
Boeings on the other hand...
Well it was general aviation (another Embraer Jet, coincidentally) as opposed to commercial, but close enough.
Still the most likely explanation is human error. There have been so many shoot downs of airlines across the world in the recent past that it is not surprising any more.
A half hearted cover for assassination is very Russian. Unlikely falls, weird car crashes, novel poisons. It’s got a long history.