What the article DOESN'T mention or acknowledge is that the only way for a terrorist organization to acquire bitcoin in large quantities is to us government controlled fiat to buy bitcoin. That transaction would be the trigger to the government that a terrorist organization is making some financial moves. It may force governments to act on suspected terrorist organizations earlier than usual, but I don't think bitcoin will enable terrorism any more than using dollars does. It's possible to counterfeit fiat...not bitcoin, which makes doing business (for a terrorist) more expensive.
They could get bitcoin via donations from supporters around the world. IS already has supporters leaving first-world countries to die in their jihad. It's completely plausible that they could collect large sums from small donations. They probably have 100s of millions of supporters throughout the world.
I agree that cash is easier for terrorists to obtain and use, but the topic wasn't about that. Governments aren't looking for a reason to ban cash. They might use a terrorist attack as an excuse to try to stop cryptocurrencies. I think the crypto community is making a mistake by pretending this isn't a real issue. I suspect it's partly because there's an overlap between people interested in crypto and people who think there's no such thing as jihadist groups trying to use terrorism to impose their beliefs on the world -- the "9/11 was an inside job" types. At any mention of terrorism or jihad, they tend to roll their eyes like it's all made up.
I'm not sure how people into crypto should be preparing for a terrorist attack partially funded by crypto. I'm also not sure how people should/will react in the aftermath of it if/when it happens. Yelling about "Building 7" (or whatever the "false flag" theory will be) probably isn't the right response IMO, but I do expect there will be a lot of that.
For the record, I think jihadist terrorism is very real. If some jihadis decide to use bitcoin or some other crypto to fund their activities, I hope they lose their private keys. And then set themselves on fire.