And Drew...I owed you and explanation as to why I thought your legal analysis was flawed. In doing that, I realize I'm talking out my posterior, as would anyone who is not on the ground in area X, experiencing these situations. With the usual caveats and disclaimers, etc., etc., let me just hit on my perception of the issues that might be presented if a human were indeed mistakenly killed by a member of one of the OP teams.
From the standpoint of a civil suit, my understanding of OK law is that the standard of proof for a plaintiff is a modified contributory negligence standard, or modified comparative negligence. As I recall, a plaintiff must show he was less than 50% negligent to recover. (As opposed to the jurisdiction where I practice, where ANY contributory negligence on the part of the plaintiff would defeat recovery) That is a pretty tough bar to clear when you are talking about a trespasser who is behaving in an (presumed) irrational and reckless way. Wantonness is a different matter alltogether, and is not subject to a comparison standard. But, I would presume OK law would require a conscious act with the knowledge that injury is likely to result, even a higher burden of proof for a plaintiff.
On the criminal side of things, we have even less of a basis to armchair Bipto's team. So much is left to the discretion of the State's Attorney to submit/not the matter to a grand jury, which may or may not return an indictment. Politics and local sentiment are a huge driver of those decisions on all sides and, sadly, budget as well. In the most general terms though, anyone is entitled to exercise deadly force in their own defense, subject to the requirement of a duty to retreat (and modified by any applicable "stand your ground" statutes). All that would matter for the shooter to successfully raise the defense is the fact they reasonably thought they were threatened. That would be on a charge of manslaughter or criminal negligence...and again, just going on general legal precepts and not based on any specific knowledge I have of OK law. Premeditation is a very poor fit for the scenarios we are discussing. Specific intent to kill an individual would need to be shown to the satisfaction of a jury. If I had to hazard a prediction, at most, discharging a firearm towards an unknown thing in the woods at night, which turned out to be a human who gets injured or killed, is equivalent to reckless endangerment, or a similar such charge under OK law.
Do these shooters run some risk in proceeding like they are? Absolutely, as nothing is for certain, but they've obviously sized up the risk/benefits and come to their obvious conclusions. One part of me would like to see the existence/not of the Wood Ape thrashed out in front of a rural jury in OK. Unless I miss my guess, you'd have many members in your venire who had either seen or heard of someone seeing such an animal and would have not the least hesitancy in pronouncing their actions reasonable. (Not since the Scopes "Monkey" trial, eh.....? ) As has been pointed out already, rural people have very little tolerance for people who lack the common sense to avoid obvious dangers, especially while trespassing. If somebody wants to plug away at sounds in the bushes (to presume how you would characterize their actions) that is their by-Gawd right as citizens, I would expect them to conclude.
On a much simpler level of analysis though, you've got to not overlook the reported outcome when the "things" were shot at by Bipto's team the first time: They came back and persisted. One, as has been reported, was wounded. Still these "things" persisted. I don't know about you, but that is a real indication to me these are not hoaxers or even humans, whatever else you might believe.