This true by legal and practical definitions. The term military means "the armed forces of a country." The armed forces of the United States include: Army, Navy, Marine Corps, Coast Guard, and Space Force per U.S.C. Title 10. They are also considered part of the uniformed services.
The Commissioned Corps of the Public Health Service is a uniformed service, not a military one. Serving in the Commissioned Corps is considered military service per U.S.C Title 42, "for the purposes of all laws administered by the Secretary of Veterans Affairs."
So, the USPHS Commissioned Corps is not a military service (NOUN) but serving in the Commissioned Corps honorably is deemed military service (VERB). This is mostly legal jargon.
Practically speaking, the USPHS Commissioned Corps isn't trained to shoot, move, and communicate across a battlefield (or water), so it doesn't make sense on a practical level to identify it as military. The Commissioned Corps is trained on basic uniformed service etiquette and protocols like standing at attention, saluting, rank structure, promotion ceremonies, etc. It is mostly trained on underserved and military healthcare, emergency and disaster response, and public health leadership.
Who cares? It's helpful to understand the Corps's identity amongst all 8 uniformed services. The layperson might see a Corps officer and assume he or she is military not recognizing the USA has an a dedicated health service for its citizens. It's also important for officer morale within the Corps to clearly understand their role amongst the services.
Now for the fun part. All of this applies most of the time. Confused yet? Read this next article to find out when exactly the USPHS Commissioned Corps is considered a military service (noun, not verb).