In fairness, before you take that bet, I was baiting you. Marathoners, tri-athletes and road cyclists have the lowest resting heart rates of any athletes. Years back, they tested NBA pros, and NFL pros against amatuer cat cyclists. There was no comparison when it came cardiovascular fitness. Some of the cat cyclists were 30% over the best V02 Max of the best of the rest. It wasn't even a contest.
Your description of your coyote induced ride sounded taxing for sure, but it's certainly nowhere near running 26 smiles, doing even a half tri, or biking 100 miles.
But most combined training competitors (as opposed to desultory ring riders) are in excellent cardiac shape, you have to be. It's not just sitting on top of the horse (really you are standing, not sitting), and there's a lot of steady muscular effort involved in just holding a horse together, plus the repetitive movement on top of a horse galloping and jumping. It's not as taxing as distance running, but some people seem to think it's "not exercise" because "the horse is doing most of the work". There's still plenty of work left over for me!
One of the things we do see is that the better you get, the less you work. A beginner will be panting and exhausted after cantering for five minutes around the ring, they really get a cardiac workout because they are constantly moving and shifting sideways and back and forth trying to keep their balance and control the horse. An experienced rider is still and balanced while cantering - much less energy expended. But riding in a three-day event (the triathlon of the horse world), or doing heavy-duty galloping and jumping for a long morning (the hounds draw the first cover at daybreak, and sometimes the field doesn't come in until noon or so) is another story.
But of course the hard riders are the elite of the sport. Since you CAN let the horse do all the work, but a bike won't move unless YOU do the work -- I agree that taking an average would put the horses generally way behind.