I think the link describes this tangentially. The minimal 10mw - 15mw current that high-five allows on a cable that hasn’t completed a handshake is enough to charge the capacitor for secure boot and trident which then can handshake with 0x74 to receive 5v 1a source. When the kernel boots the rest of the handshake process can be completed to increase the current.

That’s at least my understanding from the document.