Whatcha wanna bet he didnt have the straps on there at all or something. (Too small for the "fullsize" tires and figured they were not needed.) To "break" those 2-3" wide straps in a normal braking situation...1 of 2 things, straps were rotten, or somehow set to get cut.
I saw a 45ish mph tail waggin the dog wreck on the interstate and 1 of 2 straps broke/the other still held on the tow dolly.
Sux to be him tho...shame you didn't have 5 minutes to spare to jump out and discuss "yeah, those straps right there are supposed to go over the tires...yeah..."