The Wikipedia article is biased and naively relies on Indian state media. Singh is not a terrorist which is an easy call since he’s never committed any acts of terrorism. He’s a preacher and most of his sermons are the sort of benign stuff you’d expect (stop doing drugs, be a good member of the community, etc). Definitely a separatist but given the inhumane torture and imprisonment India has inflicted on everyday Sikh activists (see Jaggi Johal) not to mention the genocide in the 80s, separatism is probably the reasonable way out here