From a quick skim of the paper it looks like they effectively assume that implementing any 3 of those social distancing measures at the same time that Wuhan implemented their lockdown would lead to the same number of total deaths (with some adjustments).
This is less aggressive than assuming no new deaths after lockdown, but does seem quite optimistic given that the lockdown in Wuhan seems (much) more severe than school closures + travel restrictions + non-essential business closures. And this part of the model seems to be assumed rather than fit to data.
From a quick skim of the paper it looks like they effectively assume that implementing any 3 of those social distancing measures at the same time that Wuhan implemented their lockdown would lead to the same number of total deaths (with some adjustments).
This is less aggressive than assuming no new deaths after lockdown, but does seem quite optimistic given that the lockdown in Wuhan seems (much) more severe than school closures + travel restrictions + non-essential business closures. And this part of the model seems to be assumed rather than fit to data.