Is the fact that I was in the hospital protected health information? If not, why not?

It probably is today. There was a time when hospital admissions/discharges were published in the local paper.

As a population we used to be a lot less concerned with privacy. It was nicer in a way. It was a time when you didn't really worry about your identity getting leaked or stolen. If someone knew you were in the hospital, they might send you flowers or a card.

I wouldn't blame the hospital.

It was documented years ago that lawyers were buying cell phone location data from the carriers in order to drum up potential clients in hospitals.

Blame the data industry and big tech.