The first was performance, while the second is a 500TB database, and that very much requires scaling. I'm just saying it can do both well.

Ah, Postgres-XL is multi-machine, ok sure, that's scaling.

are you saying they're not related?

Only loosely in so far as bad performance can make scaling more important; however, scaling is not about performance, a super fast db could scale poorly while one that scales well could perform worse than the fast one but scale better. Scaling is about growing across machine boundaries well, so that adding more machines increases the ability to handle more load. That doesn't require good performance, it's requires good architecture.