[Renaud]

Really not the same beasts. The Cortex M4 microcontroller is self-contained with every peripheral it needs (including BT and wireless stack) and its power consumption is very small compared to a SoC.

Also, it's not booting Linux at all. For these simplish one-purpose applications, you don't want the overhead and it probably would need more than the 24k or RAM onboard the nRF52810.

They could be using Zephyr though as it supports the Cortex M4 (it's a linux-like RTOS that can be heavily customised).