Easy to dismiss as humour or hyperbole, but actually quite true. Knowing how to drive means more than just being able to get the vehicle moving.
A lot of Thais drive as though they are riding a bicycle on a country lane, especially motorcycles. Weaving around without a care in the world.
You really have to assume that they could do anything at any moment. I'm not sure how anyone can feel comfortable riding a motorbike at speed, given how likely it is for a Thai to cut them off with zero warning.