It actually looks like they can and will collect and sell data from outside of their server:

"Information From Third Party Services and Users: We collect information about the Third Party Services and Third Party Users who interact with Threads. If you interact with Threads through a Third Party Service (such as by following Threads users, interacting with Threads content, or by allowing Threads users to follow you or interact with your content), we collect information about your third-party account and profile (such as your username, profile picture, IP address, and the name of the Third Party Service on which you are registered), your content (such as when you allow Threads users to follow, like, reshare, or have mentions in your posts), and your interactions (such as when you follow, like, reshare, or have mentions in Threads posts).

We use the information we collect for Threads for the purposes described in the Meta Privacy Policy, including to provide, personalize, and improve Threads and other Meta Products (including seamless personalization of your experience across Threads and Instagram), to provide measurement, analytics and other business services (including ads), to promote safety, integrity and security, to communicate with you, and to research and innovate for social good."

https://help.instagram.com/515230437301944?helpref=faq_content

One thing they can collect are boosts. And you better believe they’ll try to associate that with an existing Facebook or Instagram based ad profile.