Hopefully, that's all it was and it'll stop showing up. It is amazing how things we put in our chickens show up in the eggs. I've heard of one person who gives their chickens so much garlic that the eggs taste like garlic.
It's probably chalazae Harmless and edible.
Other things that could be a white mass on an egg (rarer) include calcium deposits, worming drugs, and anticoccidial drugs.