I think its vary on definition about the Meaning of (Crypto-Currency) Crypto- is from the Word Cryptography and "Currency" is a Monetary Unit! the first Cryptocurrency introduce was "Bitcoin" due to its decentralized nature.The Bitcoin (BTC) was the main reference or example about the nature of cryptocurrency as (Decentralized) But since "Ripple" is not Decentralized and Controlled by Centralized Banking System its often called not a Crypto-currency! But the question is. If ripple works like Bitcoin,and other Altcoins in the same Manner as Cryptography? its also called a Cryptocurrency but not in (Decentralized way) this is just my opinion and im not and Expert regarding this topic.