The cs50 folder is not in your home directory.
It is another user's home directory.
Your userid is
ubuntu, so your home directory is
/home/ubuntu. The CS50 staff binaries are stored in
/home/cs50, which belongs to userid
ls -l to list anything in your home directory and its children, you should find that your files are owned by userid and groupid
ubuntu ubuntu. These files and directories are yours.
ls -l ~cs50 and see if you can list this other user's home directory. If you can (I'm on mobile now, so I can't test, but it should work) then you should find that these files and directories are owned by userid and groupid
cs50 cs50. These files are not yours!