That simply is not true.
From the Initiative 1639 FAQ webpage of the Washington Attorney General:
Do Washington’s background check requirements violate privacy protections for firearms purchasers’ medical information such as HIPAA?
No. Under Washington law, a signed application to purchase a pistol constitutes a waiver of confidentiality and written request that the Health Care Authority, mental health institutions, and other health care facilities release, to an inquiring court or law enforcement agency, information relevant to the applicant's eligibility to purchase a pistol. Effective July 1, 2019, that waiver of confidentiality provision is expanded to include applications to purchase a semiautomatic assault rifle.
No. Under Washington law, a signed application to purchase a pistol constitutes a waiver of confidentiality and written request that the Health Care Authority, mental health institutions, and other health care facilities release, to an inquiring court or law enforcement agency, information relevant to the applicant's eligibility to purchase a pistol. Effective July 1, 2019, that waiver of confidentiality provision is expanded to include applications to purchase a semiautomatic assault rifle.
On the webpage, the word "law" in "Under Washington law,..." is a link to RCW 9.41.094
https://www.atg.wa.gov/initiative-1639#15 hipaa
My conclusion is that the waiver on an application to buy a weapon is absolutely a valid waiver of HIPAA privacy protections. However, (and this is my opinion, based on my research) the information sought is limited to that information contained in health records that would make one a person who cannot legally own a firearm. That definition and that information sounds to me like it is quite limited; for instance, an involuntary commitment or a not guilty by reason of insanity would be relevant, and a heart attack would not be relevant and would not (in theory) be reported. It even sounds like the records generated by an attempt at suicide would not be relevant, since that doesn't make one a prohibited person.
Furthermore, it also sounds like there is a chance that the government would ask "can this person own a gun?" and the records people would say "yes" or "no", and no medical information at all would be transferred. That remains to be seen, as the exact mechanisms and procedures are established. This scenario may be a pipe dream, but I can't imagine a sheriff's department that has 12 deputies dealing with the mountain of work that reading just my records would entail, let alone half a dozen folks like me.
BSA1, I don't know where you are getting your information from, but it is simply incorrect.
