I'm confused here, there are twitch drops, but by default XBox Ones stream to Mixer. Is this some sort of goof on somebody's part?
Just wondering.
It's not a "goof".
'Twitch drops' is a service provided by Twitch, not Mixer or Rare or Microsoft. Hence, it's only applicable by watching Twitch streams. You can download the Twitch app on Xbox if you don't have it and watch a participating stream.
There have been times in the past when the drops were for watching on Mixer using their 'Mixer Loot' service (which weren't on Twitch), it just depends which company is running the promotion.
I hope this clears up your confusion.