I did this on our first night trip. Daughter and wife went, "left side lights are on".Thank you I suspect you are right about the switch position. I have had the car for a long time but I have not driven it much lately and forgot about the switch position for off is straight up.
I went back in and flicked the switch. Then they went, "now its the right side".
I thought, "oh dear have to go home withour diner before the battery runs dry".
And then I looked at the switch.
I bet it has caused a many a flat battery, when the intention seem to have been to prevent them.