It's unclear if the man was hit by the buffalo's charge, but he was able to walk away without obvious injury — hopefully having learned a valuable lesson respecting wildlife. But what he did isn't just unwise, it's also probably illegal.
According to the Fish and Wildlife Service, which oversees the refuge, "harassing wildlife is prohibited," and for good reason. Getting too close can cause undue stress to wild animals, triggering responses that are potentially harmful to people or themselves. Unfortunately, not everyone has gotten the message.