QStandardPaths: XDG_RUNTIME_DIR not set, defaulting to '/tmp/runtime-aadithyasb'

I was able to find what the caused the terminal to issue the warning. Yet I am posting this so that it would be useful for people someday who are new to using WSL like me. This link helped me to solve it and gave me a better insight on how linux works under a WSL:

https://dev.to/winebaths/getting-up-and-running-with-the-windows-subsystem-for-linux-8oc

To solve this issue I just added the below lines to my .bashrc file:

export XDG_RUNTIME_DIR=/some/directory/you/specify 
export RUNLEVEL=3

After this just run the command

source .bashrc 

Now the warning will not keep displaying in your terminal.