It also works in a sentence such as "so and so won the popular vote but lost the election", which seems to be about the most common use of the term, while Mendel's meaning doesn't (even if, as you say, he's technically correct).
Mendel's meaning of "popular vote" is the same as yours. But he's merely providing the additional snippet of information that even the American system is indirectly based on a popular vote. What you're saying is the same in reverse order -- i.e. the well-known fact that in the American system "winning the popular vote" does not directly determine the final outcome. But you guys are all nonetheless using basically the same meaning of the term "popular vote".
Word salad galore!