I concur. If you are concerned about catching it during your travels, people who don't have it are just as irrelevant as the number of automobiles who don't have it; thus, cases per people is just as irrelevant as cases per (people + automobiles).

You should be concerned about the fraction of land area on which you are at high risk. If 100 people have it, and each person creates a high risk across A area (and the areas don't overlap), that is 100*A / country-area. Which is proportional to cases/area (presuming A is constant) the first statistic he used.

EDIT: if you know you are going to interact with N people, the cases per population figure is relevant again.