You should never try to rescue a drowning person (exception perhaps: small child) unless you have a floatation device with you to keep between them and you to assist them with. Or they WILL take you down with them.
The old guy was right whether or not he couldn't swim (which in LOS he probably couldn't).
The lack of swimming training in Thai schools is a catastrophe. Drowning used to be the biggest killer of children in the UK before they started teaching us at school. Very rare occurrence now. See it all too often in Thai news though.
All it took was an easily installed solid plastic type tank, 3'6" deep, 15x20 meters, and some changing rooms with benches and lockers. Oh yeah, and a pile of plastifoam floats. So cheap. So easy to install. Junior school, aged 8. But younger were taught. Can't remember feeling cold so it must have been heated in some way.
They taught hundreds of us through the years. I went on to be a competition swimmer and diver.