I was exposed to a definition more similar to what's on the quiz only when working overseas for a company staffed mostly by Brits and that's what they called out staff mailboxes.
In medieval times pigeons were kept for meat, and their cotes were often attached to the houses. A small opening in the wall made it possible to feed and water them or grab one for dinner. In the 1700s desks were made with small compartments which had doors resembling the openings to the earlier pigeon "holes" in the wall, and they came to be known as pigeonholes. It became a verb in the mid-1800s meaning to classify or compartmentalize something.
The average number of words native English speaker use is estimated at 20,000 to 30,000 but, there are over 1,025,109 words in the language (and growing) so we shouldn't expect to know them all.
And ofcourse it makes you think of moonshine.