[johnnny]

Where did you get the idea that anybody on the Internet can?

The first step to network booting (PXE or UEFI boot) requires DHCP, which means a DHCP server or relay on your local broadcast domain (switched LAN, and I'm sure there are extensions for boot-over-WIFI somewhere).

Sure your computer could fetch the boot image over the Internet, if you're okay with involving the unreliability of the Internet in your boot process, but that'd require explicit configuration on your DHCP server.