Although the film is supposedly set in Ireland and the bus drives on the left, the passenger door is on the right. Anybody alighting from the bus would step down into traffic, giving away the fact that the bus is from a country that drives on the right.
In the entire film, only two motor vehicles are seen. One is a bus with the passenger door on the wrong side for use in Ireland. The other is supposedly a French tourist car. This was presumably easier than sourcing right-hand drive vehicles as would be found in Ireland.