It's Asahi Lina who really did the kernel driver (building on Alyssa's reverse engineering work).
Mostly based on her own reverse engineering work actually (which was all livestreamed). Alyssa's work was on the shader ISA and what goes into the various command queues to get the GPU to do useful things, Lina's work was on the lower level aspects of how the queues even work, interactions with the firmware, power management, etc.
They use all the same tools etc. But given Asahi Lina has chosen not to reveal their identity it's better to just assume it's a different person.