What do you mean by "Americans"?
I mean the ones who talk, behave and generally are American. As for language, barely any of them can string a sentence together in Polish. And yes, I've spent quite a bit of time hanging out in their dorms, so I know a thing or two about them - although I always hung out with the Asians.
There are also English language programs in dentistry, pharmacy, and physiotherapy.
All of those programs are known for passing Americans without troubling them in Poznan.
how can you be certain they are a medical student, not a student from Mickiewicz or even just a kid traveling?
If you're from Poznan, I'm sure you know the BP garage near the university, near Rondo Przybylskiego. When you see a group of drunken ******** in there, speaking loudly in English with a deep South accent, it's a certainty that they are in fact American and studying at the university.