So the answer is - possibly. I know this is going to sound a little odd, but it depends on whether or not the chiropractor bills "electronically" for the care he provides. If it is a cash business or he sends in claims to insurance companies, Medicare etc. by the US mail, then its possible the practice isn't covered by HIPAA.
The behavior that has been reported to you by your friend certainly sounds odd and I'd recommend trying to ask the practitioner about it directly to see what he says and if the matter can be resolved that way. If not, you can report it to the federal Office for Civil Rights via the process described at the link I am including below. There is also a lot more information about HIPAA on the same website.
This response is intended to provide general information, but not legal advice. The response may be different if there are other or different facts than those included in the original question. See MKnutsonLaw.com for more information on why this communication is not privileged or create an attorney-client relationship.