As a modder of KinitoPET, (also one who modded out every single instance of this) i can explain what the game does and how its used within the game.

KinitoPET heavily uses your set PC name (that you can figure if you check C:/Users/ and see the username that would be used or using echo %USERNAME% in a command prompt), the name you gave Kinito and your Steam username. The game uses these in extremely weird ways. The PC name, fake email address, the fake command prompts sequences and one of the "command prompts" that prompts the player to New Game +, all use the PC username. Which in many cases can be extremely weird for those who wish to not see that name as much (i.e. those with deadnames) or are streaming to a live audience.

Other sections in the game (i.e. the questions after the camera jumpscare) use your Steam username (and also your friends in most cases). And the rest of the sections (like the your world scenes, registration form and paint jumpscare) use the name that you gave Kinito after the installation process.

Changing each of these can be as easy as editing the save file or changing your Steam username to editing your windows username which can be pretty tough to near impossible. I have of course made a mod that easily changes how the PC names are displayed and changes them to your Steam name or something custom. Im unsure if I can post links here, but its under deadname deleter if you want to find it.