A bit vague what the prosecutor is actually charging them with, but apparently they consider some forms "radical sovereignty" to be "terrorism".
Because they found a crossbow, some ammo and a large number of ... documents about radical sovereignty.
I'm not inclined to give the prosecutor the benefit of the doubt here. Until they prove otherwise I will assuming they're being hysterical. There were other cases recently where they used the T-word overzealously.
https://nos.nl/artikel/2538748-stel-opgepakt-op-verdenking-van-deelname-aan-terreurorganisatie-van-soevereinen