Did I some how aquire tank herpes?

At no point in my life have I ever bought duckweed. But I seem to... have... duckweed? Logic tells me it hitched a ride on one of my new plants. But the fanciful part of me can't help but feel I've been cursed by the aquarium gods. Tell me oh wet benevolent ones! What did I do to offend you so completely!?!