I think it might be, there’s no way Anakin would be able to buy proprietary hardware or software. So either he stole it, which his mother probably would not have allowed. Or he was able to scrap all the parts together because there is a template for humanoid protocol droids that we have also seen round Star Wars. And then the software itself either Anakin programed entirely himself, (which I know he’s very smart, but even that seems a stretch) or he forked it. So it would make more sense that there was an open source catalog of protocol droid software. It also would make more sense due to the fact that a lot of people have droids, but they are not all created equal. I would think many of the droids on Coruscant were proprietary, while many of the droids in the outer rim are open source.
I think the reality is that Anakin was written as a tech wizard by writers that saw a lot of technology as just magic that tech wizards can do.
He was able to build a droid out of spare parts not because there was an open protocol droid system that enables technically inclined people to learn how to build their own custom versions. He built a droid because that’s what a child tech genius would do. How did he program it? More tech magic. He’s impressive, you aren’t supposed to understand anything of what he did, it was just a plot device to show what the chosen one was capable of before the Jedi even found him.
Not trying to be a wet blanket, just so much of technology in media is written this way.
Especially with star wars, where it’s closer to “space fantasy” than “science fiction”