The GNOME Foundation provides the GNU Image Manipulation Program community and developers with services like fiscal sponsorship, technical infrastructure, promotion, and copyright assignment.
The GNU Image Manipulation Program is not a GNU project; it’s just called that way, just like GNOME’s acronym expanded to GNU Network Object Model Environment back in the day, but it was never part of the GNU project per se.
You can read the issue between GNOME and the FSF on the topic you linked; the Foundation has been pretty clear that the statements made over the years by Richard Stallman, while he was president of the Free Software Foundation, were not compatible with the values and goals of the GNOME project; the latest ones, in 2019, which also led to Richard resigning from the position of president of the FSF were merely the last straw.
As for the GNU project: GNOME is not part of GNU, though we focus on the same goal of a free-as-in-software-freedom operating system aimed at all users. GNOME has, and always had, its own infrastructure, rules, and governance, distinct from the GNU project.