Already did.
"building with 50 floors" is irrelevant. Stop trying to divert. You mentioned a person in a grocery store. Let's stick with that. After a person with COVID enters that store, COVID is eventually in the air everywhere in that store. It doesn't matter whether you stand next to the person or are on the other end of the store.
Continued attempts to divert. The convo is about a COVID-infected person spending time inside of a grocery store and how that affects someone else who later walks into that same store.
The virus is in the air everywhere inside of that grocery store.