The referral URLs on my Analytics page all show itch.io links, including my profile page and some of my works' relevant tags, so, for the time being, it looks like all my referrals are currently internal.
Viewing post in Any Way of Finding Who Collected Your Work?
Collections are also itch links, yeah. But they'll only show in your referrals if someone actually clicked through to your page through the collection, which isn't super common, especially in a private collection. I wouldn't worry about it, it's just funny trivia.
It's also worth noting that people don't need to actually own or play your game to add your stuff to a collection.