I received a Fancy pattern Vivillon today. But it was a girl, to my suprise. Serebii.net said it would be a boy, so is it a glitch or am I just overlooking things?
You misread it :). On the site it has that it will be either Male or Female not one specific gender. So no there is not a glitch, every event where a Pokemon can be either gender in-game has always been able to be recieved either Male or Female.
Hope I helped!