I dont know if expats are better owners or not, but it is general thing you find in advertisements here.
Normally it is considered that expats keep their cars in better condition and drive more carefully. However, with expat population here at 80% or so, it is more of a norm that a car is expat-owned than otherwise.
I would think that most asians probably keep their cars in better condition than other expats, but this is not a general categorization. Same goes for Europe. You see many ads about "british-expats" selling a car...I do not understand whats special there as british owned cars normally are not better than others..maybe their own british self-esteem that their cars are better! but that part is rubbish.
Also, the lady-driven thing is also rubbish if you see how many ladies drive here!
The only things that probably does make sense from a vehicles condition perspective are:
1- Service History - If a car has been serviced regularly, it will be in good condition.
2- Accidents - If the car has not been in any major accidents. Small bumper fenders etc are fine if they are fixed and did not damage the rest of the car.
3- Offroad driving - This is specially for 4x4 vehicles. A vehicle taken to the desert normally will have gone through some rough driving in low gears, at high RPM, under-body injuries, sand in the engine etc. It is incorrectly thought that locals always do offroading and expats dont. I think the ratio of locals/expats offroading their 4x4 is pretty much the same.
Phew! that was longer than I though
Hope its helpful!