I distinctly remember going to Italy, asking for a pepperoni pizza, getting a pizza with only red peppers on it, then being told that "pepperoni" just means bell pepper in Italian, and that the sausage is actually an American invention. Then smacking myself because the word is actually so obvious.
It's weird that they would call the sausage pepper+oni which rather obviously means big pepper, rather than a variation on "salciccia" which obviously means sausage, but the deed is done and everyone is stuck with that confusion now.
Anyway, I guess that means the answer is both and pepperoni purism is fucked? Imagine being Italian and being asked for a pepper pizza "but only the pepper, no [foreign word for pepper]" and having to cut up sausage for some reason.
PS: maybe it's actually a good sign if you get peppers when explicitly asking for only pepperoni: it must mean someone with passing knowledge of Italian works there