True. But we generally don't accept colloquial answers in most of the cases.
But this magazine is called "Gość Niedzielny". It would be abbreviated to "Gość" only when speaker and listener know what "Gość" they are talking about.
I would know as I have them in a binder
labelled as Gosc
cheers thank for your kind message
Polskie przysłowie -- Gość w dom, Bóg w dom.
A Polish proverb -- Guest in the house, God is the house.
W Wikisłowniku piszą że znaczenie jest "gościnność jest świętym obowiązkiem gospodarza".
In Wikisłownik (Wiktionary in Polish) they give this explanation of the meaning, "hospitality is a sacred obligation of the host".
This is probably old Polish and does not follow rules of grammar exactly ;) I am not sure but it may be just a shorter form of "w domu" or it may be from "do domu" but with Russian grammar since part of Poland was under Russian rule more than 100 years.