the Berasit Hebrew Dictionary

שתימ

Based on etymological clues, the most likely meaning of 'setim' is a group of people who were descendants of set (aka Seth)

Due to the timelines and the narrative of most people being wiped out by the flood, this interpretation is somewhat flawed in that everyone after the flood would necessarily be a Sethite, since Noah was descended from Seth.

It might be that rather than a strictly biological descendance, what is referred to here is a cultural characteristic, or a particular tradition that people could opt in to. In other words, the Sethites may have been followers of Seth by way of some traditional knowledge, story, or perhaps arcane teachings.

see also seti

LexID 98147