Yes, as the 12” Macbook with a ~5W TDP chip manages without a fan, I’m sure a slower general airflow together with that heatsink works well for the 7W chip in the 2018 MBA.

And when looking closer - the vents on either side of the antenna bracket, that the fan exhausts through on one side - air is drawn in on the other side and then guided by the vanes in the ventilation holes, allowing it to flow easily from right to left (when viewing bottom/inside of the MBA) over the heatsink cooling fins. There doesn’t appear to be any other openings in the chassi, so Apple has probably designed the airflow pretty efficiently in this fashion.

Pretty cool! Only Mac laptop I’ve seen with a fan but without heat-pipes/sinks by the fan.