tl;dr: There are two types of bloom, sugar and fat. Both result from storing the chocolate wrong, leading to either fat or sugar crystallizing on the surface of the chocolate. And both types influence the texture and taste somewhat but are completely harmless from a health perspective.
Personally I don't understand how this can happen. Who stores their chocolate long enough?
Its too good to just eat because she wants some chocolate, so it sits there... and sits there... and sits there... while we throw a family block in the trolley each week when we do groceries.
We get so much chocolate at Halloween. I'm not a big candy guy (pastries for me, thank you), and I'm sure as hell not letting my kids have unrestricted access to caffeine and sugar. We almost always have some left when the next Halloween rolls around. If I have a piece in September it will likely have bloom on it.