Turns out it was just standard 8N1 115200-baud UART.
I didn't see any mention of this proprietary UART protocol in your blog and the GitHub project looks like it was as simple as reflashing the onboard ESP32 once everything is wired correctly?
Maybe things at Meta have changed after their "year of efficiency" but week one would be orientation and the start of boot camp and he wouldn't normally already be on a team this soon. I'm calling BS and taking this as an amusing work of fiction.
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