You never know what you'll find when exploring an old abandoned house. This one has mice who are suffering from post traumatic stress disorder. See, while Cinderella got her prince and lived happily ever after, the mice were the collateral damage of the fairy godmother's magic, and they were left with lifelong scars. You get the idea this talking mouse has waited a long time to spill his guts to someone who would listen. Yeah, it's funny, and beautifully animated, but it also gives us a minute to step outside our normal perspective and consider the psychological damage left behind in the fairy godmother's victims.
The sequence is also different from the usual in that it doesn't have a setup or exposition, or even a conclusion, leaving the impression that it could have been clipped from the middle of a longer story. But then you realize all that isn't totally necessary. We don't really need to know who these people are or why they are there. Why make a two-minute story into a ten-minute story when you don't have to?