In Linux boot order, the kernel will execute /sbin/init, however, I can see another file /init existing in the file system on my linux (CentOS 8 WSL2, Ubuntu 20 WSL2).
They are different binaries:
$ diff /init /sbin/init
Binary files /init and /sbin/init differ
What are the differences between /sbin/init and /init?
/usr/sbin/init or /sbin/init is the executable starting the SysV initialization system. For compatibility reason, when systemd is installed, it's an alias to an executable of the systemd world.
The executable /init is unusual, in a Linux system. I suggest to investigate the reasons why it's present. It could be the part of a malware.
You mentioned WSL 2. Microsoft still runs special Linux kernel inside VM and because the goal is not to strictly emulate they introduced own custom init process: like what's the point to start cron/cups/X/etc in every distro you installed.
Microsoft altered init process to avoid useless resource consumption (according to expected use cases of WSL 2).
When you import a Linux distro image Microsoft adds own file /init which is shared among all distros!
Even more: according to How does WSL/WSL2/WSLg work without systemd? WSL 2 is utilizing a single VM to run all distros. So the kernel is the same and the instance of the kernel in memory is shared, separation is done though Linux namespaces.
