This was pre-Web, and it involved mail-order adventures, and you were kinda alone.
IIRC, he got the book in the gift shop at the Oregon Museum of Science and Industry, on a school field trip. Just getting access to the initial information was almost random.
Then one of the most obvious components -- the motors with the right gearing and power requirements and weight properties -- weren't at Radio Shack, and not something you were likely to be able to cannibalize from a yard sale.
So first you needed to order a catalog from a company known to sell the motors in single quantities. Then, once it arrived, weeks later (eons in kid perception of time), you needed to convince parents that it's a good idea to write a check or use their credit card, to order these expensive parts from some weird mail-order company they've never heard of. (And probably none of their friends have their kids doing this.)
And there are no forums where you can talk to other people doing this. And no influencer YouTube channels showing other people succeeding at it. All you have is this one book, and dubious parents.
Then you needed a bunch of hobby-shop supplies, like various sheets of balsa wood, rods, etc.
In absence of printable STL files, and cutting patterns, and PCB layouts you can send off, and affiliate links, or parts kits, if you stick with it, you eventually scrap a lot of supplies building the mechanics to something that looks minimally viable.
And you eventually risk plugging in your first soldered circuit board into the family's only home computer (no, you don't have a hobby/educational microcontroller SBC). And if it zaps, you might not have anything to program on for a long time.
If it doesn't zap the family computer, then you try to get the mechanics not to rip themselves apart.
So a kid of that era who embarked on the project might never get a working robot, but they would learn a lot about a breadth of things, in the process of trying.