Having had a prominent hand in raising two kids, one of whom is still a monstrous little two-year-old, I can say this is actually a safe and practical method for dealing with this sort of situation.
Yes, I know it looks bad, but I bet the kid will move his ass the next time mom says it's time to go.
Not all kids need a leash, but some do. There are kids who, if their hand is released even for a second, will run as far and fast as they can wreaking havoc and destruction before they are caught. They are often too young to understand discipline. You can yell at them or even spank them but it will make no difference. A tether is the only thing that works.
My younger nephew has to be leashed. Hopefully, he'll grow out of it next year.