*shuts down LogicAI* huh, that was unexpected. Don't worry, he only brought a knife to cut his cookie into more pieces to share it with you. :)
Jokes aside, if you wanna know how the game knows your name, it's using a pretty simple function in gamemaker. enviorment_get_variable(STRING).
It is used for debugging mostly, and to save files on your PC (such as savefiles) but if you want to, you can acces literally almost every variable on the PC (that wouldn't cause harm to the machine ofc as GM is a sandboxed engine). If your replace STRING with "USERNAME" it will get the PC's username.
Here's an example of the code:
*//text LogicAI says
textboxtxt = "Hello," + enviorment_get_variable("USERNAME") + "!"*
That code would return:
Hello, *your name*!