I think the idea is that POST creates a record (and in theory fails if that record already exists). I guess the commenter above is saying that if you inverted that (fail when the record doesn't exist, return the record if it does) it would be similar to QUERY? Not sure if I agree with that, but PUT's return semantics are a bit vague.. it often returns partial or combined records, or just a 200 OK (with or without a response body), or 204 No Content for unchanged records (with or without a response body)

It's clear what POST returns, so... perhaps QUERY is more similar to it in that sense?

Whatever the original intent was, POST definitely does not return a new record consistently in most actual APIs. It's frequently used for actions that don't conceptually create anything at all.

PUT is the idempotent one. POST typically performs an action; PUT just creates-or-updates.