This was my reaction as well and left me wondering if there is missing information here.

NYC has been on lockdown for weeks. A very large percentage of the city is staying home. Some completely isolated, but most are not completely isolated.

People have periodic contact with family, friends, neighbors, pharmacies, grocery stores, and/or delivery people. People who live in buildings with shared common areas (doors, entryways, elevators, mail rooms, laundry rooms, ventilation systems, etc.) cannot help but risk some exposure. Masks and social distancing are not 100% effective.