I'd like to point out that most of the demonstrations where there's been problems (I think calling them violent is an exageration, and also its origin is largely disputed as many blame the police) have nothing to do with Tsunami Democràtic.

Tsunami Democràtic's goal is to encourage and coordinate massive civil disobedience and protests, and that's what they've done so far. Their app even has a check box about non-violence you are forced to to log in. It's hard to imagine how they came to the conclusion that this is a terrorist organization except if you take into account the political views of the Spanish government and all its branches and Tsunami Democràtic.