Yes, it does seem strange. They might have just said the autopsy results are inconclusive. Maybe they know something about the case that they haven't revealed.
The missing teeth seems difficult to explain without foul play. I can see the severed head and moving of the spinal cord elsewhere maybe being animal predation plus decomp but I don't see the teeth being knocked out that way.
The jawbone and lower teeth are missing from that skull. Not sure if that means it was found separate from the rest of the skull, not found at all, or removed by the coroner.
Bottom line here is the fact he texted his mother beforehand saying he was being chased by a bunch of white men and feared for his life, then turns up somewhere in pieces, makes this a compelling case for homicide. It would be quite a coincidence if he sent those texts then just happened to die in some other manner.
Bear in mind, however, that the police might not be able to find the killers, even if they do their best investigative work. It's always going to complicate a murder case when the body is found months later and has been ravaged by predation. Even Crump's "independent autopsy," while concluding the the death was a homicide, could not provide a more specific cause of death (i.e. blunt force, stabbing, shooting etc.) When a corpse is in that condition, the chances of solving the crime go way down.