I'm skeptical of this. Something as simple as knowing the meaning of curb painting color, turning on red, or knowing when to move past an emergency or other special vehicle requires non-universal knowledge of regulations, sometimes hyper-local. The idea that nothing they do would be affected by country-specific regulations is dubious.
They're only in a few hyper-local areas.
Taking a driver's test, and knowing the meanings of road symbols are two different things. At no time did I imply the workers are completely ignorant of locale-specific driving details- I imagine they receive extensive training on this, but do not take a driver's test per se.