That just sounds like some food experts have chosen to use the word "rancid" for a technical measure which is actually at odds with the meaning of the word in common usage. This is a common behaviour of experts, but it's patronising and doesn't really help anyone.
I don't know the etymology, but I think it's more likely that the colloquial definition of "rancid" evolved from the condition of rancidity in other oils, such as animal fats, that render them unpleasant and smelly, as opposed to just tasting different (as in the case of olive oil).
Yes, the unsaturated portion of the oil is most subject to oxidation from the environment, like from the oxygen in the air which acts more rapidly at warm storage temperatures than cold storage.
The expert odor committees are condemning oils that have an amount of oxidation that is so low it is hard for them to all agree so their consensus is the most accurate overall judgement.
Ordinary chefs are not likely to even notice such a slight amount of degradation.
This is a far cry from highly oxidized cooking oil like you sometimes have in fast-food operations who wait until it's long overdue to replace the oil in their fryers. This can often be so rancid you can smell it from quite a distance, anyone can agree about it, and any oil which is only a small fraction as bad doesn't earn the qualification as "rancid" by ordinary people.
And plenty of them go back for second helpings anyway.
