Nevermind, I discovered that this is a technique called pxechain.
Citando Rodrigo Abrantes Antunes <rodrigoantunes at pelotas.ifsul.edu.br>:
>
> Hi, I need to have two pxelinux servers In the same subnet, is there
> a way to create an entry in the menu in one of them that point to
> the other?
>