I do a lot of off-leash hiking, but mostly in high desert terrain where the visability is better & not in forests.
I have had many hikes w coyote encounters. In general, the coyotes will run away. A 40 pound coyote is no match for a male ridgie. That is not to say that your boy could not have been in a fight w more than one coyote. Alternatively, since you evidently did not actually see the fight, perhaps, he fought something other than a coyote. In my opinion, since your boy is neutered, the only likely reason that a coyote or even a small pack of coyotes would fight a comparatively large male ridgie rather than flee is if they were defending a den-site that perhaps he stumbled upon.
I will share with you an experience I had a few years back. I was hiking with my RR male, Roo, & my mix, Abby. Roo is 90 pounds & Abby 80, so they are much larger than coyotes. At the time Roo was unneutered since he was being shown. He came over a hill & then the two of them just bolted from me on chase. They were after a female coyote. I was nervous because you do hear about females luring pets. Anyways, I am calling & huffing & puffing after them. After about five minutes Abby returns. Eventually, Roo comes back to me as well. Ten to fifteen minutes can feel like forever under those circumstances. I get them close to me & we hike out. The next week I do the exact same hike. I see the exact same coyote, but this time she is closer & making warning sounds. My dogs stay w me & do not chase. They understood her warnings. We hike out & away. The coyote cautiously follows at a distance & behind her is a cub. So evidently, during the first hike, the female was behind the densite & luring my dogs away. The second week she was at the den site & willing to defend. I believe those two hikes provide great insight into coyote behavior.
Anyways, back to your question, if it it were me, I would keep my dog on-leash & very close, & try to get him back into the woods w positive re-inforcement until he felt comfortable.
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