I view it as being OSS or postgresql dev that happens to work at microsoft. I've been doing the former for much longer (starting somewhere between 2005 and 2008, depending on how you count) than the latter (2019-12).
Perhaps you’re not familiar with what NSA historically stood for: Never Say Anything.
Let's say agency A has some scanning capability on open source software that detected this backdoor attempt by agency B. If they had gone public, agency B now knows they have this ability. So agency B will adjust their ways the next time and the scanning capability becomes less useful. While if agency A had told Microsoft to "find" this by accident, nobody would know about their scanning capability. And the next attempt by agency B would only try to avoid having the performance impact this first attempt had, probably leaving it visible to agency A.
no this engineer is world-known for being core PostgreSQL, a team with high standards.. unlike that company you mention
It was reported by an MS engineer who happens to be involved in another OSS project. MS is doing business with the US intelligence community, for example there is the Skype story: First, rumors that NSA offers a lot of money for people who can break Skype's E2E encryption, then MS buys Skype, then MS changes Skype's client to not be E2E encrypted any more and to use MS servers instead of peer to peer, allowing undetectable wiretapping of arbitrary connections.
But it's a quite credible story too that it was just a random discovery. Even if it was the NSA, why would they hide that capability. It doesn't take much to run a script to compare git state with uploaded source tarballs in distros like Debian (Debian has separate tarballs for the source and the source with Debian patches applied).