"Possibly carcinogenic" in WHO terms basically means "someone once did a study that may have found a possible link, so we can't prove that it's totally not carcinogenic".

To put it in starker contrast, there is a category that is "probably not carcinogenic." There is literally nothing on that list.

It was a thing a several years ago - a study found an association between higher consumption of pickled foods and some GI cancers.