folk vs social group

folk and social group both are nouns.

Word	Noun	Adjective	Verb	Adverb
folk	Yes	No	No	No
social group	Yes	No	No	No

As nouns, social group is a hypernym of folk; that is, social group is a word with a broader meaning than folk:

folk (noun)	social group (noun)
the traditional and typically anonymous music that is an expression of the life of people in a community	people sharing some social relation
people in general (often used in the plural)
a social division of (usually preliterate) people
people descended from a common ancestor