> Does every mention of an Open Source library or project morally require attribution to the original authors or something?

No. But in my view had this been written by an independent journalist, they would describe it as "TensorFlow by Google". The project is virtually completely driven by Google, so "By Google" is a more distinguishing classification than "Open Source". We can speculate but strong impression is that Amazon doesn't want to give kudus to Google.

Not sure that Google would agree. Looking to Google's own words about open sourcing the project:

"We hope to build an active open source community that drives the future of this library, both by providing feedback and by actively contributing to the source code."

No, lol. The license stipulates the conditions, and the common licenses only have the condition that the code or final product make the attribution somewhere in the GUI.