This is likely standard and comes with Discourse.
Specifically:
We use this information strictly to personalise your experience in this community, as well as to associate the posts you make to your user account. During the registration step you were asked to provide a username and email address, you can also optionally provide additional information to complete your user profile on this website.
We retain this information for the life of your user account, and you are able to withdraw consent at any time by deleting your account. At any time you may request a copy of your contribution to this website, via your Rights & Consent page.
This is just telling you that your username will be associated with your posts.
Occasionally, we may send emails to your registered email address in order to provide updates and/or to notify you of new activity that is pertinent to you. You can customise the frequency of the community digest (including disabling it outright), as well as select which types of notifications to receive via email, via your user settings page. Unless explicitly changed in your user settings, this community delivers email digests every .
This is telling you that you will get email notifications from the forum.
There is nothing being harvested here. You don't see this when you sign up for a phpbb forum, but they do it anyway - Discourse is just more explicit.
