I also saw that comment and laughed. However, I really don’t think it is a good comparison at all. It’s more just funny to think about.
How about a smoking section on an airplane or in a restaurant?
Man I miss those.
It fails to capture the exponential nature of the possible disease spread, and while disgusting, pee in the pool isn't actually dangerous, but it does get the idea across that you can't confine things where you don't have walls to confine them, which is the main point. As metaphors go, it's not terrible, since we're short on metaphors that do capture the exponential nature.