Thanks for posting this.
The problem with xylitol is it's not required to be listed as an ingredient and can be found in many products, like antacids, not only peanut butter. It's used because it's a sugar alcohol and found naturally in many fruits and veggies. For humans, it's a much better alternative to fake sweeteners and it is considered "natural".
I no longer give my dogs anything other than fresh fruit, veggies and foods made specifically for them. You just never know.