Right, but medicine is part of science.... would you argue that a Physics major isn't in STEM because P is not one of the letters of STEM?

No, it isn't; Biology is a part of science. Medicine is, as DuskStar put it, "[Science/]STEM adjacent".

How is it not a part of science? What does a field need to have to be included in STEM?

Just because there are other skills needed besides science based ones doesn't mean it isn't a science field.

It's obviously not a 'basic' science though and other applied sciences that are uncontroversially included in STEM get their own letter (engineering and technology).

People differ in whether they think medicine and the other applied sciences fall under the 'science' umbrella or not. Try searching around and you'll see a lot of mixed opinions on the subject.

I guess you could argue that Tech and Eng getting their own letter means they don't fit under the "S" in STEM, so STEM might not include the non-enumerated applied sciences. (Nor fields of "applied technology", like trucking.)

Right I definitely knew it was math (have 2 engineering degrees myself :) )...but still assumed it was commonly assumed to fall on the spectrum of STEM (definitely on the opposite end from say...physics...but still on the spectrum).

How can anyone get a qualifying score on the MCAT without significant exposure to science?

Disclaimer: I'm definitely coming at this from a U.S. point of view which someone mentioned in another comment effectively (not always but definitely in the overwhelming majority of cases) requires STEM undergrad degrees to get into medicine.

Some branches of medical research are basic sciences (eg endocrinology), and some are applied sciences (those broadly construed as 'health science', eg dietetics). But the practice of medicine in a clinical setting (healthcare) is both a science and an art (ie a skill learned by practicing it), and I think most would say that the knowledge it requires is scientific but much of the day-to-day work is an art.

So people tend to disagree about where to put medicine. But overall, most major public institutions in the US don't include medicine in STEM:

* US Department of Labor (Bureau of Labor Statistics) -- No. (https://www.bls.gov/careeroutlook/2007/spring/art04.pdf)

* US Department of Commerce (Economics and Statistics Administration) -- No. (https://files.eric.ed.gov/fulltext/ED522129.pdf)

* NSF -- No. "The National Science Foundation is a United States government agency that supports fundamental research and education in all the non-medical fields of science and engineering."