A 6 node cache and caching in DynamoDB, what the hell happened to the industry? Or people just call every kind of non business-object persistence cache now?

I don't understand your comment.

If you're given the requirement of highly available, how do you not end up with at least 3 nodes? I wouldn't consider a single region to be HA but I could see that argument as being paranoid.

A cache is just a store for things that expire after a while that take load of your persistent store. It's inherently eventually consistent and supposed to help you scale reads. Whatever you use for storage is irrelevant to the concept of offloading reads