I see where you are coming from, and you are *technically* right
Mickey is an anthropomorphic mouse-
and Furries are classified as anthropomorphic animals, and/or people who cosplay as such.
So by technicality, yes, Mickey is a furry in the sense of his design. However, I like to note that furries usually adhere to a typical style of art, with their fur and muzzles and complexity often following a pattern, in which Mickey is not included.
Just in the way that all squares are rectangles, but not all rectangles are squares.
All furries are anthro animals, but not all anthro animals are furries.