This first Mishna in Shabbat (2a) describes the transfer of an item from a private domain to a public domain. The Mishna describes the individuals involved in this transfer as
העני עומד בחוץ ובעל הבית בפנים
The poor person stands outside, in the public domain, and the homeowner stands inside, in the private domain.
There are many other labels which could have been used including generic names (eg Reuven and Shimon) labels related to the act (machnis/motzi). Why did the Mishna choose to use the specific labels of poor person and homeowner?