I used to think so too, but `unit` is more dedicated to a part of some separated part of a building. Here, it's more about direct access from the street to the store, and `addr:door` seems like a better-fitting tag.

Regardless of the ambiguity between `addr:door` and `addr:unit`, adding a value that specifies the apartment number in the building to `addr:housenumber` is definitely an error.