This is an interesting question that I wondered about too.

Here's why I think it works: you have a mix of things picked up by such an indicator, including spikes in takeout traffic as people are sent to get pizzas...

You probably also pick up things like delivery drivers / doordash etc coming in and out collecting orders.

Ultimately the proof is sort of in the pudding on this indicator: it captured the pre-strike frenzy of activity.