Actually, I think that unusual questions by visitors pop up frequently.
I also have been asked how much a particular piece of art costs, while
working in a museum.  One day I was asked by a man who quietly
asked, "Are these paintings for sale?  The labels use the word
purchase, so I really don't know".  I realized that the labels did indeed use
the word "purchase", but to indicate that the painting was "purchased"
by the museum using a donor's gift.  I gently explained to the visitor that
the painting was bought by the museum, and that I understood that the
word "purchase" could seem confusing.  I had never thought of it before,
and he was right.

All too often museum professionals forget that many questions, which
strike us as funny, are very serious to those who ask them.  Many times
a visitor has never been to a museum before, and the experience is
confusing.  These questions are very precious, and while they make us
chuckle afterwards, should always be treated seriously.  It is refreshing
that visitors ask questions, even if they are a little unusual.