The SAR teams searched all the trails between where the horse was found and Nicola Ranch. There's a sizeable mountain in between, and major highways, so the possible routes are fairly limited.
KR, the tracker who retrieved the horse, declared he knew all those trails and the horse couldn't have come that way without leaving tracks that he would have seen, so the searchers were wasting their time.
I think early on, he went and seached for any tracks on the Nicola Ranch side of the mountain, the possible trails there are very limited because of the Coquihalla [ETA, there's only one or two places to cross under the highway from Nicola Ranch): "I would say it is almost 100 per cent impossible for anybody to leave that ranch and try and hide their tracks and be successful.”
Missing cowboy leaves no trace - Merritt Herald
He didn't say that police/SAR should be searching somewhere else. I know some people might see his words as implicating him, but my interpretation is he knew what he was talking about, and knew very quickly that it was no accident, and the only way the horse could have gotten there was by trailer. He complained about the hours-long delay in identifying who the horse belonged to, in a place where people and horses don't go missing: "When they called me back at 12:30 p.m. — this really pissed me off — they told me that it was the manager of the Nicola Ranch’s horse, who had been missing since Saturday night. I don’t know why nobody knew.”
UPDATE: Ben Tyner confirmed missing by Nicola Ranch - Merritt Herald