The bios flaw they were exploring was the bios having flawed anti DMA protections.

From the article

According to the company, the Input-Output Memory Management Unit (IOMMU), which protects system RAM from Direct Memory Access (DMA) devices, is not fully initializing upon boot in some motherboard models. This means that even though the BIOS might indicate that Pre-Boot DMA Protection is active, it’s not actually protecting the entire system.