How do people who do things like this - get the time to do it? Did he do it in his personal time with or without a job? If anyone else does something like this - can you give your insights. I would love to be able to do something like this.
It should be pretty standard for CS undergrads to be at least familiar with some ISA.
edit: undergrand -> undergrad
PS: I highly recommend Patterson and Hennessy Computer Organization and Architecture (pick the Arm, RISCV or MIPS edition... any will do) to actually learn about all these things and more.
Some of them have gone on to be names you've heard of.