Wow you are lucky, maybe the low engine speed saved you there.
I remember my brother buying a secondhand Ford Escort diesel and told him to make sure the cam belt had been replaced before buying it. A new belt was fitted and I then told him to have it replaced every 40,000 miles.
A couple of months later he mentioned that the belt had again been replaced, “ You’ve clocked up 40,000 miles in a few months?”.......”No just 4000 miles”