ECB has some vested interest in bringing down bitcoin or POW mining to be precise. They have already created a certain proposals for the EU countries which are still being debated but the motto of the proposal is to ban any type of POW cryptocurrency from the soil of EU. So it's no wonder that ECB is making statements essentially demeaning bitcoin and cryptocurrency in general.

However, these are speculations! It will definitely be tough if the ban proposal is passed in EU parliament. But even then, that will be temporary. As EU miners will shut down, the difficulty will reduce. So a lot of old miners from different parts of the world may come back into action to fill in the blank. So I personally don't see a reason to belive in ECB and its statements.