First, the paper finds that Americans overwhelmingly changed their behavior — measured here through restaurant visits — before official lockdown measures went into effect. The policies did have a marginal impact on top of what was already happening, but most of the decline in economic activity happened simply because people got scared and stayed home. (They are not the first to find this, of course.)
But by contrast, when states reopened, many of us jumped at the chance to go out again. This effect is clearest in a chart based on Yelp data:
By the time lockdowns went into effect, restaurant reservations were already nearly nonexistent. But within a few weeks after reopening, they’d regained more than half their original volume.
As the authors write, two different things are probably going on here. First, while lockdowns had little impact right when they went into effect — because no one was going out anyway — the explosion of activity at the end of lockdown suggests they did have an impact later. (That is, some of the increase would have happened earlier if the restaurants had been legally allowed to seat guests.) And second, some people probably took the very act of reopening as a signal that it was safe to go out again.