This is a bit wrong for Thailand as it doesn't mention nicknames. Or rules for using the given name vs. nicknames. Unless in very formal context it's normal to use nicknames not given names. In day to day life nicknames are by far more commonly used than given names. Family names are almost never used expect in legal documents or formal setting. It's common for people who have been friends for years to not know each…
In 2001, I did a month long exchange program to Thailand. A group of eight Canadians stayed with eight Thais, and the year before they stayed with us. Incredible program.
All the Thais, as you mention, had nicknames. But many of the nicknames were English words that weren't really used as names in the West. I lived with a guy named 'Knight'. Another guy was 'Farm'.
Were these names Anglicized versions of Thai nicknames? Or were the actual nicknames just sometimes pulled at random from an English dictionary?