Yeah, this is specific to the Google Messages app. For now, anyway.

To add to this, Fossify just released their phone app. It hasn’t hit the repos yet, but it’s on their github.

The Fossify forks of simple apps should be coming soon too, if you want to stick with something familiar. They’ve already released their calendar, gallery, and file manager, the rest should be ready pretty soon.

This is most likely something that someone else gave out, not OP. Some old school “friend” signed up for some app and shared their phone contacts, app proceeds to spam those contacts hoping for more sign-ups.