There's a huge difference about the first video and the second one (the kick) and the difference is the horse's body language. The first horse looks playful, ears foward, interested in her play and seems to be in a good mood. Plus she has a huge safe distance, which is really important! The second horse is the combination of frustrated horse (because he's just trying to get the treats) with a girl who is encouraging that kind of behavior by giving him treats without even realizing the language of the horse. The horse has is ears pinned back all the time. She's just ignoring it and no safe distance. So yeah, huge difference in the behavior of both horses and people.
I do trick training with my horse and one thing that makes me really upset is when people find something funny that the horse is doing without even realizing what is really happening. Just like in that video. The girl in the second video finds really funny that the horse is jumping behind her and following her around, woww, really nice, what a shame she learnt her lesson in the worst way possible. People HAVE to pay attention to horses body language because that's the only way they have to communicate with us and tell us if there's something wrong or right.
So yeah, first video is totally fine for me, she seems she knows what she's doing, safe distance, happy horse, it's just a play in the padock :) Second video, hmmm, what a complete disaster!