Importantly, zoning is intentionally mixed, so a significant fraction of the population doesn't drive for much of anything unless they choose to move way into the suburbs and it is a very neighborhood-y city. When a building goes in, the lower floor is often restaurants/bars/retail/etc to allow everything to be local. This is important because Seattle's highways are at max capacity and they can't be expanded anymore due to geological limitations (surrounded by water, no unused land remaining). The only way to continue the insane pace of population growth is to build up in a way that minimizes the amount of driving required, so that is how they have been dealing with it.
Tech companies in Seattle are clustered in a few different neighborhoods, but most of them are walkable from their respective neighborhoods. That said, tech companies are slowly migrating toward the greater downtown area due to the gravitational pull of techies that want to live there. And everything in the greater downtown area is walkable if you don't mind walking (and people in Seattle don't). It isn't a small area.
Microsoft specifically, though, is still mostly on the "east side" (the metro area has a 88 square kilometer lake in the middle, Seattle proper is between the "west side" of the lake and the bay). Microsoft has offices in the major urban neighborhoods but still have a huge campus in Redmond (an east side suburb).
It's still summer.
Your friend is in for quite a surprise, especially in January when the latitude means sunrise at 10 AM, sunset at 3 PM.
Lack of income tax in Seattle/Washington is huge if you make tech wages. My mortgage in downtown Seattle is less than the additional income taxes I would pay if I lived in California!