He's not very good at explanation in that video. In fact he falls right into the exact problems he says are used as evidence. He starts out with people are terrible witnesses, and then goes into his explaining based entirely on witness drawings/testimony/stories whatever.
'Stories say the ropen eats dead bodies', so he bases his morphological discussion on the basis of his assuming that's all they eat (in fact he directly says that he assumes that's all they eat as the basis for the discussion). If they exist, they could be scavenging bodies and not solely subsiding on them. Eating bodies would probably be highly notable by the local populations if witnessed, but a creature eating plants or fish or whatever is not notable. He jumps from the idea that they can eat bodies to the idea that all they eat are bodies.
They could also not be eating bodies at all and the idea of them doing so could be pure folk tale and false, for example later Trey talks about the 'leg boy' cut from his mothers leg that became the sun in dealing with the place of the ropen in local mythology. I presume no little boys were cut from their mother's leg and became the sun. But since Trey's starting position is acceptance of the tales of ropen eating bodies, he would logically have to accept 'leg boy' becoming the sun, or any other local myth. Trey concludes that the hypothetical ropen couldn't exist because it couldn't eat bodies as sole sustenance. The parallel conclusion would be that the sun does not exist because leg boys can't turn into the sun. I am pretty sure the sun exists.
'It's long tail makes it unsuitable for flight', he is once again relying on witness testimony when his opening argument is that witness testimony is terribly unreliable. He also (around 14:20 minute mark) emails an "actual pterosaur expert" (a paleontologist) about the long tail and posts the person's responses in his video.
Unfortunately for Trey, his chosen expert's response begins with "We know a lot of long tailed pterosaurs had crests now,". According to the expert, there were indeed pterosaurs with long tails even if they did not have the crest the ropen is supposed to have. The expert also says that a long tail may be good or bad depending on the flight characteristics and the creature's lifestyle. Trey's position was that the ropen's reported long tail made it an impossible creature, something his expert's statements contradict.
'It glows' while there are no other tetrapods that glow. Maybe it doesn't actually glow at all, but 'glows' because it's seen high in the air around dusk, when it's still in the sunlight while the observer is not. We've seen this effect recently with the various rocket contrails getting reported as alien rays or ufos or whatnot in the press, but you don't have to be nearly that high up to be in the sunlight while the observer is not in order to 'glow' from reflected sunlight with nothing around you to make it look like you are actually glowing.
'It's not a surviving pterosaur'. Ok fine. I'll accept that. What if it's not that but something else that happens to look similar because it occupies a similar ecological niche. He looks at a "ropen video" and declares it to be a frigate bird. Which of course the creature is the video most likely is. Unfortunately for Trey there's a problem with his identifying the creature in the video as a frigate bird (and not for example, saying it was CGI).
The problem is that he admits the video is of a real creature, even if it's not a "ropen". He identifies it as a frigate bird, but that's a problem because the frigate bird has a relatively long tail, relatively large wingspan, and a known ability to stay aloft for weeks at a time. That's a problem because Trey has already concluded that the ropen's long tail makes it an impossible creature, yet he is identifying the video of a long tailed flying creature as a real creature.
He's saying that something that an observer identifies as a ropen exists, even if it's not a "ropen". If the hypothetical ropen was a competitor for the same ecological niche, it would likely look broadly similar to a frigate bird. It's a problem of a rose by any other name.
While the ropen most likely does not exist of course, his explanation for why it is not real is poor and purely reliant on the same things that he starts his video are saying are unreliable, and the conclusions he comes to such as the tail are both contradicted by the his choice of actual expertise on the subject and his own acknowledgement of a creature with the morphology he says is impossible.
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Frigate birds in flight, the most likely explanation for a ropen:
