There's a profile of the dude in Wired that goes over what made him so valuable in Larry Page's eyes.
https://www.wired.com/story/god-is-a-bot-and-anthony-levando...Basically, he was one of the key founders of the project that made Google Maps what it is today (a crown jewel of Google with one of the best cartography datasets), vs what it was originally (better UI to third-party, licensed cartography data).
I remember about 12 years ago somebody from the GIS industry, scoffing at the notion that Google might even try to go do some mapping of their own. For him, maps was something Navteq and TeleAtlas knew how to do, and a search engine was deeply misguided if it thought it could venture into that space. That was honestly the prevailing wisdom at the time — it was going to be hard for web-based Google to even deal with the ugly real-world-ness of mapping.
Fast forward to today. Google Maps basically showed the GIS crowd how their work oughta have been done all this time. They invented street cars, street view, and actually made it work; and they used the data to produce accurate maps of the world.
So to your question, what led this guy to an astounding level of monetary reward was that he was part of a team that made a big, calculated bet with Maps and executed very, very well on it. That gave Page ample reason to compensate them well, and it gave him trust that they could handle more projects where they would show up incumbents (such as the traditional car manufacturers, whose inroads into self-driving tech had been very timid for decades).
And it's not clear that they are close to self driving cars, but they certainly contributed to upping the game of that whole industry.
So there's your recipe :) I'd bet that folks who came up with the key tech behind the iPhone are in similar positions at Apple, given how they turned the whole mobile phone business on its head (remember Nokia?).
EDIT: I don't mean the above to indicate that the reward was deserved in any way. Likely, a lot of what happened here is luck plus outstanding team work rather than individual lead performance. But to the question being asked, this is the kind of circumstance and outcome that seems to have supported, in one man's view at least (Page), that level of compensation. If you look at folks at Google who made/make big $, the story is often similar - they led products that were fledgling challengers into industry leaders within a few years (Chrome, Android...).