I believe what she's saying is that most of the horses we think of as wild are actually feral. The mustangs and the island ponies are all feral. There have not been wild horses in North America in...a very long time. I'd have to look it up. Many thousands of years. The feral horses are all descended from domesticated horses that ran loose.
The only wild horses left, I believe, are in Asia, and are very few in number.