I remember running the MS-DOS 6.22 defrag while in Windows 95, rebooting, and finding nothing worked afterwards because DOS didn't support long file names. Needed a complete reinstall.
If you recognize what's happening here, you're part of a generation that also spent endless hours fine-tuning autoexec.bat and config.sys files.
And if you're not sure what's going on in the video, I honestly envy your youth.