If you read the actual report, you'll see that's exactly (a part of) what they said:
A further category of innovations is digital currencies, such as
Bitcoin, Litecoin and Ripple. The key difference between these
and local currencies is that the exchange rate between digital
currencies and other currencies is not fixed. Digital currencies
are not at present widely used as a medium of exchange.
Instead, their popularity largely derives from their ability to
serve as an asset class. As such they may have more
conceptual similarities to commodities, such as gold, than
money. Digital currencies also differ from the other
technologies discussed so far in this box because they can be
created out of nothing, albeit at pre-determined rates. In
contrast, local currencies come into circulation only when
exchanged for pounds sterling. While the amount of money
held in e-money accounts or local currencies depends entirely
on demand, the supply of digital currencies is typically limited.
This paragraph is the only mention of digital currencies in the 10-page "introduction to money".