Is Azure's confidential computing essentially encrypted RAM?
The article you are referencing mentions encrypted RAM but that was only a reference to possibilities of enhancing the technology more in the future, not about the current state of confidential computing.
Confidential computing means, that when data is in use these things are prevented:


Malicious insiders with administrative privilege or direct access to hardware on which it is being processed

Hackers and malware that exploit bugs in the operating system, application, or hypervisor

Third parties accessing it without their consent



according to Microsoft own announcement
So in other words, it is kind of equivalent to encryption and firewall that are seen in communication but this time applied to running programs in a Trusted Execution Environment (TEE), which the term for the area which is protected when server runs a program.