I think digital currencies is include all thing that we use as payment in digital transaction, even it is fiat, or anything else that we can use as payment, it can be called digital currency. But crypto is i can't explain about crypto, but like bitcoin and others of it.
Yes it is, Digital currency and cryptocurrency is both useful on digital media however the main difference is that Digital currency can be a coverted fiat like Dollars, won stored at online wallet for example Paypal and Cryptocurrency is a currency in a form of cryptography like BITCOIN and ETHEREUM. However, we both coined it as digital currency often since we are using it on digital world.