https://www.bleepingcomputer.com/news/microsoft/windows-10-tests-wsl2-linux-kernel-updates-via-windows-update/

In the latest Windows 10 Insider build, Microsoft has started to test the distribution of Windows Subsystem for Linux version 2 kernels via Windows Update. 

When Microsoft announced WSL2, they explained that all WSL2 distributions would use a real Microsoft-compiled Linux kernel based on the stable 4.19 version release of Linux at Kernel.org.