I think perhaps what's being described is akin to a bulletin board with fliers outside the doctors office, with general advice to the public, not specific directed advice to a patient about their specific health issues. I'm not sure that falls afoul of HIPAA, I would imagine it doesn't since it's not specific at all.

At the same time, that also makes it irrelevant to the point at hand, since it's not Facebook messenger at all, just general health posts and items offered by that medical group.