It does automatically set for some columns (e.g. with all values as 0, another properly sorted)

So i took the docs at face value

sorry, this was my bad - the data type of the column was wrong (specified as STRING while it was an INT), so the ingestion job did not correctly derive it as sorted

I'm quite curious now though. If you call the segment metadata endpoint and pass in the name of that column, doe it show that it has a sorted index? http://localhost:9000/help#/Segment/getServerMetadata https://docs.pinot.apache.org/basics/getting-started/frequent-questions/ingestion-faq#how-to-apply-an-inverted-index-to-existing-segments