Yes. correct, it was back a couple of months after release Asobo even told us they “improved AA”, etc, etc. It was actually CAS.
However, it is not the only feature from that API that they use for their in-house engine. Lots of features are part of the GPUopen, and together with Gameworks middleware by nVidia it is an open standard that studios such as Asobo make extensive use of.
Those can often be and in fact are features not often exposed through the final product’s UI that work at the lower levels, for example quite good radix sorting algorithm by AMD for the parallelization of various functions in a title, efficient multithreading for up to 4 workers in DX11, etc.
Or the reflections for example, a studio can use the present sampling via monte carlo rendering and perform the depth tracing (ray marching) - but then use a very good AMD’s SSSR to shade the surfaces with exact evaluation of materials…plus you can go with low res source reflections with just 2x2 or 4x4 tiles in the screen-space for all types of rays in the scene, yet still get the nice looking reflections coz that approach supports using FSR directly on source reflections mid-process. The ones in the sim are maybe created using a similar or the same comb of tech.
Studios build their in-hose engines and solutions and use a number of features, tools whatnot…be it in Unity or UE whatever…tools by Pixar, Nvidia, opengpu…from all sides.
I like the fact Asobo uses 3ds max and Babylon…when it comes to modelling, materials and all that stuff for MSFS…I mean it’s one of my favorite repositories.
Yes, there is no official FSR implementation, that is true.
I have some great news to share with you, at least with all of you who didn’t already hear about it:
The next big thing in the (should be March) version of AMD Adrenaline driver will be - FSR! 
Indeed, so they managed to place their spatial upscaler and the algo and all the tech for the in-driver activation on basically any title. So even if a game doesn’t have FSR integrated natively, we will be able to activate the feature from the upcoming Adrenaline driver suite.
Theere is the minimum requirement (as AMD says) in that the GPU architecture has to be based on RDNA. They obviously have some difficulties with GCN…but let’s hope it also works on those cards.
Another novelty with that driver will be introduction of the AI based eye/gaze and head tracking. All you need is a webcam with depth sensing or that Kine…ct (?) or something. Same one that Windows Hello requires.
The technology in the upcoming AMD Adrenaline suite comes from the AMD’s partnership with Eyeware. Let’s hope it finds good use in the simulator ! 
More about it you can check out here —> Eyeware | Head & Eye Tracker Software Tech - Webcams & 3D Cameras
[EDIT]
I completely forgot!
I took to trying and testing out the FSR, as it is available as an open source now.
This is how NYC looks with FSR enabled and set at Ultra (the “worst” quality where it takes 1080p and upscales to 4K):
For those of you who are not, I encourage you to leave your DLSS feedback there instead of here. The Community team reads a lot of posts in the forums, but right now, all eyes are on the beta category.