I think Terry Pratchett has a similar passage in The Fifth Elephant - this axe, over time may need a replacement head, or the handle may need some work, but it will always be the same axe that my father gave to me [paraphrased].
I guess, applied here, it's a similar thing to knowing you are male in a female body for instance. Morphology of the avatar in your head can be different to your external appearance, ie. you always had large boobs?