It's more that definitions are made with an assumption of normal market conditions but what's happened in the DRAM market is extreme. Production of conventional DRAM package types has evaporated, while the demand is unchanged or increasing, because of new demand for HBM which is even more profitable.

So some common sense is required: yes under normal circumstances selling below the market price is dumping, but when the market price looks like a vertical line because of a sudden shock then you can't really take the market price too seriously. Mostly the price of DRAM is not set on the open market but is negotiated via contracts between the major players so there isn't really one price of DRAM at the moment. If you're a big customer like Apple you can get a price that is completely different from what you or I can get fighting for scraps on eBay.