Didn't realize their entire MySQL data layer runs in AWS. Given that they went with basically a blue-green update strategy, this was, essentially a "witness our cloud spend" kind of post.
It's neither. I remember them moving to the cloud but apparently they moved to Google/Oracle (the latter making this article particularly interesting btw). As per the relevant press release : "It’s understood that Uber will close down its own on-premises data centers and move the entirety of its information technology workloads to Oracle and Google Cloud."