Oh by the way it looks like currency just means to "run or flow" in it's etymology, or "true meaning".
And it looks like the modern definition is something like ..
"noun, plural currencies. 1. something that is used as a medium of exchange; money."
So.. not sure where you got your definition, but I'd say steem fits the definition of a currency. I would suggest even stocks are form of currency. Basically anything that is used to trade for another thing is currency.
In ancient times and even today you could say "cattle" are currency, or various other animals or things that are traded for other things.