If it looks like I'm being cautious, it's because I am; I cut two or three minutes of both me approaching the horse and the horse walking in my general direction. I'll take that as it giving me permission to get close.
I don't know what the knot on its leg is, but it looked like it'd been there on purpose, I'm not the owner so I don't know if it'd trust me to touch its legs, and while uncomfortable the horse looked used to it. That, and not wanting to get in trouble with the horse's owner.