I’ve installed LAMMPS (August), already build files and set path. However, the “lmp” version shows as 20 Nov 2019. Since I use WSL (on window), I’m not sure that is this problem related to WSL.
The problem is due to you lack of Linux/Unix knowledge. Unlike on Windows, on a Linux/Unix shell the current directory is not searched for executables (it is a serious security and consistency problem).
So the executable you pick up has been installed elsewhere and is in a folder that is in the PATH environment. You can find out with “type lmp” where the second case executable is located.