General Discussion

The person who is firing the missile or dropping the bomb would not even know they were hitting Wager forces. As far as the person firing is concerned, they could be hitting Ukranian targets. In contrast, the folks on the ground getting blown up would have a pretty good idea of what hit them and where the attacks or missiles were coming from.

It is possible that it was friendly fire given how poorly Wagner was coordinating with the Russian military, but as you note, if it was a sustained bombardment, then it gets a bit murky.

Finally, if you were either Prygozin or the Defense Minister, wouldn't you feel that you would need to kill the other in order to survive. Russian politics can be deadly:

https://www.businessinsider.com/list-of-people-putin-is-suspected-of-assassinating-2016-3