Brownian motion in models for virus spread? Was reading a Washington Post article "Why outbreaks like coronavirus
spread exponentially, and how to flatten the curve” and it looked like they were using Brownian Motion.

(Can't directly link the graphic, but it's the third graphic in the article, showing particles bouncing around, but I've included a screenshot:)



If this is the case, how do particles in a fluid medium resemble interactions in a human population?
I read this article when it came out. I don't think the point is about whether or not people behave like particles in a fluid medium, but about how quickly people can spread the coronavirus when randomly interacting with one another in an open space (in my opinion, this model would be a reasonably good representation for a crowded area like a mall lobby or a beach where people are moving around more or less randomly).

However, even in other settings when people aren't moving around randomly, if anything, people are more likely to interact with each other in restricted spaces like sidewalks where there is less choice of where to position yourself spatially.