Who cares about "real currency"?! It's irrelevant here.

Say you own a bunch of coal. Some guy tells you that if you "invest" your coal with him he'll return 7% of it per-week risk free. He returns a bit and then he vanishes with all your coal.

The fact that coal is not a currency is irrelevant. Its something valuable to you and you got scammed out of it by a phony investment.