After all, a horse rider is usually termed a “jockey”.
It’s best to email them the suggestion.
I agree that it should be counted as a synonym, but a jockey is specifically a horse racing rider, no?
Yeah, indeed, but I’ve heard it being used casually to refer to all horse riders, regardless of racer status
yes, if you do a quick image search on google 騎手 brings up images of horse riders of all sorts, including jockeys. Jisho also has “jockey” as a possible translation. Though, there’s also ジョッキー if you wanna be specific, I suspect.
Also, while we’re nitpicking
Most people refer to it as horseback riding, こういちさん
Doubtful, if you ask me. But they could add it as an acceptable synonym if it isn’t already. Looking into it, it’s a difference between American and British English.