You're right, "people" can sometimes be used with an "s".
FR stated the most common usage of "people" but then didn't go on to explain that "people" can also be used to express a group of persons under a common culture, race, nation etc. So in this sense I can talk of "my people" (e.g. The U.K.) and you can talk of "your people" (e.g. The USA) and we can also talk of "our peoples" (meaning the two separate groups) while still referring to the fact the two groups are different.
Got it
Peoples in effect groups of groups of people
Or as I recall a reporter commenting on a large gathering 'We have peoples from around the world here today'
Thanks again