If you read the detailed specs on the page closely it never advertised 5.0 speeds _on the PCIe slots_ only on the M.2 interfaces. The top line product name is deceptive, either intentionally or accidentally.

Full expansion card specs only mention PCIe 4.0: https://www.memoryexpress.com/Products/MX00129652#:~:text=en...

M.2 Storage specs mention the 5.0 speeds and only for one of the slots: https://www.memoryexpress.com/Products/MX00129652#:~:text=pr...