I wish they had used the word "map" in place of "hash" throughout this entire article. The use of hashes is an implementation detail and wholly irrelevant.
My comment was meant tongue in cheek. Maps are _the_ universal data structure: they can be used to map any input to any output. The rest is just an implementation detail.
One might even call them "functions", but that ruins the joke.
Not in this case. An ordered map implemented as a tree has the same interface but with very different operation complexities