Ok, you win. "Cryptographic hash" is not the formally correct terminology. I hang my head in shame. What I find interesting is that you dig up a quotation that says exactly what I've been telling you, but with different words, and use it to claim that I'm wrong.
I wasn't quoting the RFC. It's interesting that they used almost the same language I did.
You seem to think that your quotation says MD5 is a digital signature. It does not. It's telling you that MD5 can be used as part of a digital signature protocol.
You also seem to think that the RFC is giving you a comprehensive list of all the allowable uses of MD5. It's not. It says "MD5 is part of this complete breakfast," but you don't have to eat it that way. If you want to learn what you should eat for breakfast, you have to study nutrition, not breakfast cereal advertisements.