It is a reference to "Winnie the Pooh", a highly regarded children's book, by A. A. Milne.
Owl is the most learned creature in the Hundred Acre Wood, since he knows how to spell (although badly, he spells his own name WOL). He also doesn't know how to spell TUESDAY correctly, but since none of the other animals can either, and at least he can distinguish it from WEDNESDAY, this is thought to be quite an accomplishment.
(As an idiomatic expression it would equivalent to "one must respect someone who can do something you can't, even if they might do it badly").