My read of that is, "he's going to have some free time but we will always be accessible to him and trained." That's about the best they can do without chaining him to a chaperone 24/7, which he would hate at 13. Hopefully they provide maps of where the stations are.
I tend to doubt he will ever be 100% solo at the park. He will probably stick with a buddy or two, who he has hopefully oriented to his diabetes at least a little bit. In a setting like an amusement park, lows in Nowheresville From Anything are the most dangerous possibility we need to be ready for, IMHO. If someone he hangs out with knows that a non-diet pop works for a low in a pinch, and your son is willing to ask his buddies for a hand if he needs to, he'll likely be fine.