So, I ran into the three horseback riders again today, and the girl who let pet her horse before, does seem to be ignoring me on purpose. The other two were friendly like usual, although they did say they taking the horses "for a quick ride" so we just chatted a tiny little as they rode past, but the other girl just started looking at her phone, and never even acknowledged me. After they went by, I remembered that she was like that other times I ran into them, before the first time we ran into each other and she let me pet her horse, and even the last time, after we met the day before, she kept going past me after the other two stopped to talk, and didn't stop and come over by us until I thanked her for letting her pet her horse the day before. So I don't think it's because of anything I did either of the times I talked to her.