The "he" in the hints is just there as an example - you need to replace it as necessary with the subject of the sentence. In this case, the only noun or pronoun in there is "das Pferd", so it's that that's doing the running. You would need an "er" in there if "he" was running.
again the fast & slow speakers are saying different words!!!!!!!!!!!!!!!
This is tricky. I just made a mistake with the verb and Duo did not notice. The audio is dreadful, I was trying to work out any verb to fit a horse. Maybe that is why Duo let it pass, unless r is normally pronounced as a variant of w (news to me). And my horse? Erm, ask Duo!