ethnic group vs grouping

ethnic group and grouping both are nouns.

Word	Noun	Adjective	Verb	Adverb
ethnic group	Yes	No	No	No
grouping	Yes	No	No	No

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

ethnic group: people of the same race or nationality who share a distinctive culture
grouping: any number of entities (members) considered as a unit

Other hypernyms of ethnic group include group.

ethnic group (noun)	grouping (noun)
people of the same race or nationality who share a distinctive culture	any number of entities (members) considered as a unit
	the activity of putting things together in groups
	a system for classifying things into groups