But it has reason only for M.2 cards in the variants A, B, E and M when PCIe pins are used.
Librem 5 has only SDIO, USB 2.0 I2S and UART connected to BT WiFi M.2 slot (even that E-key allows PCIe) and other Key B slot for modem with only PCM, UM used for SIM, USB 2.0 and some GPIOs (in the fact I2C) for some modem specific control…
So no PCIe pin connect to any of there slots.
You can find my analysis of Librem 5 hardware and presentation there
more with recording but in Czech only sorry