Netflix still uses AWS for much of their support systems (billing, discovery, etc. etc.) The core business of delivering video is not on AWS and has never been. That runs on their in-house CDN, OpenConnect.
The history is that mainly they used well-known CDNs for streaming, followed by their OpenConnect CDN network now. AWS has always been used for metadata.
I believe this is inaccurate, Netflix was streaming from AWS in their early years IIRC.