If you look at the second photo in the sequence there's a brown and white horse in the distance that I'd wager horse No. 1 wished he could go a-wanderin' with.
So does it matter if the brown horse was actually fenced in? A scientist would say yes; a letter-of-the-law Bible thumper would say yes; a news reporter would join them. Actually, the Bible thumper might say it was God's plan for the horse to FEEL fenced in, but that's a topic for another day.
Your creative blogger, your imaginative, freewheeling commuter, however, he or she could be just as comfortable going with a made-up version of the story -- in this case one based on a strong hunch.
So I'd have to say the "Hey, I wanna play, too" scenario is not just plausible, but a convincing version of the truth. As they teach referees, step back, take in a broad field of vision, call what you see and, right or wrong, sell your call. I saw this horse very interested in what the other horse was doing. If I were the horse and felt the same way, wouldn't I gallop off and join him if I could?
Case closed, horse fenced in. That's my story, and I'm stickin' to it. Since there's no instant replay in photo-blogging, all decisions of the referee are final.