I wonder if he asked them what they were doing there, they told him the FM gave them permission and he pulled his phone out to try to call and verify. And either Ms. Badass lost it and charged him - like, “How dare you question me?” - or the dog got out at that point and attacked him. And then the gun appeared - I’m still not convinced MB brought it to the scene but also not convinced that he didn’t bring it - and RG jumped him and the gun discharged during the scuffle.
As for the alleged “murder plot” - didn’t they come up with that theory after the shooting? I seem to recall something about LK stating that it became clear afterwards that what they had been hearing on the recordings was a “plan” to dispose of them (for the purpose of stealing her horses - yeah, right. ).