If you check out the graph in the article, the sales drop was sharp, abrupt, and coincided with the outbreaks: https://b.fastcompany.net/multisite_files/fastcompany/imagec...

Anecdotally, I definitely heard the outbreak discussed frequently here in NY -- probably because I regularly eat there, and so did my friends (up until the outbreak anyway). Maybe you didn't since your friend circle stopped eating there before the outbreak?