"Yes, it is possible to get carbon monoxide (CO) poisoning while running your car with the air conditioning on and the windows down, although the risk is lower compared to having the windows closed.
Here are some key points to consider:
Source of Carbon Monoxide: CO is produced by the combustion of fuel in the engine. If the car is running, it can emit CO, especially if the engine is not functioning efficiently or if there is a leak in the exhaust system.
Ventilation: Having the windows down allows for some ventilation, which can help disperse CO. However, if you're parked in an enclosed space (like a garage) or in an area with poor air circulation, the concentration of CO can still rise.
Air Conditioner Use: When the AC is on, it typically recirculates air from inside the vehicle. If CO enters the cabin, it may not be effectively diluted by outside air, increasing the risk of exposure.
Symptoms of CO Poisoning: Be aware of symptoms such as headache, dizziness, weakness, nausea, and confusion. If you experience these while in a running vehicle, it's important to exit the car and seek fresh air immediately.
To minimize the risk of CO poisoning, it’s best to avoid running the engine in enclosed spaces and to ensure that the vehicle’s exhaust system is in good condition."
https://www.quora.com/If-you-are-running-your-car-with-the-AC-on-and-your-windows-are-down-a-little-can-you-still-get-carbon-monoxide-poisoning
"Mr. Patcharin, the vehicle owner and Mr. Ekgarat’s employer, explained that the driver had been employed for just over a month and had reported frequent illnesses."
If he had existing relevant medical conditions he would have been more vulnerable to CO.
Existing or not, his reports may well have been an indicator that all was not well with the exhaust system.