They probably didn't have a legal motorcycle license.
I don't know what gets into these people that don't ride motorcycles in their own country but when they get to Thailand, they think it's easy and they can handle it. I've had an motorcycle since I was a teenager but I think Thailand is not a regular or normal place to ride a motorcycle let alone learning how to ride one.
Food for though: Thailand is ranked one in the world for motorcycle accidents.
https://www.bikesrepublic.com/featured/10-countries-with-the-highest-proportion-motorcycle-related-deaths/