Indeed, however if it entered Russian air space without permission, then the Russians may have a legal basis to shoot it down or at least challenge it. .
I think rather than simply jumping to that conclusion, we explore different options, but yes it does seem to be pointing towards an assassination OR attempted, not confirmed the wagner leader was even on board.
Russia isn't going to admit to an assassination, what it will do is try and find a justification for shooting down an aircraft in this case.
It seems from the BBC it was enroute to StPetersburg so not sure where the origin was ( I am sure this has been stated, just can't remember), but why would prigozhin be in russia knowing he was a wanted person?