because Poe wrote on both!

Yay that is the one answer...

read the poem the raven that's what i had to do understand the riddle

Lewis carrol had no intentions of the question having an answer. It was suppossed to be unanswerable because he wanted Hatter to be wasting time. So assigning the riddle an answer would really ruin the special element that the riddle has.
Hence, why hatter replied "I haven't the slightest idea"