If one delivery guy gets it and is busy driving around neighborhoods asymptomatic for weeks the delivery would cause spread. If one grocer gets it and is busy running his store asymptomatic for weeks then many who visits could get it. So its just luck.
The goal with these measures is to buy time for hospitals. And they both will.
The social distancing stuff makes sure flow to the hospital is not as high as it would be if everyone was not social distancing. What matters at the end of the day is how many free beds are at the hospital and what plans they have to handle overflow. Korean hospitals had plans on how to coordinate with each other and between regions for docs/equipment etc to handle overflow/overload.