The ones we recorded tpd us the folk songs were different from other types they knew of and may have even sung - ie music hall, Victorian parlour songs, early pop songs etc.
They often used different terminology - my Daddy's songs (even though they may not have learned them from the family), come-all-ye's - fireside songs, (in the case of the Travellers 'Traveller's songs (which included standard folk songs) or simply the old songs.
Walter Pardon used the term folk songs and was catergorising them as early as 1948 when he started writing his family's songs down in a notebook. We have half a dozen tapes of him talking at length on the differences between all his types of song.
See my article on Musical Traditions web-site on the subject under the title 'By Another Name' in the Enthusiasms section.
Jim Carroll