This tells us nothing about how it was turned off, only that the routes were withdrawn from the global routing table. Which isn't "how" it was turned off, by why it's stopped working.
There's some guesses in here, but the title is rather misleading. No one still knows why these routes are no longer being advertised, only that they're not.
Considering Syria is saying cables were cut even though Cloudfare pointed out 4 cables would have had to been cut simultaneously with a couple being under sea it's seriously doubtful this is what happened. The only plausible explanation is that the traffic was stopped and given Syria's reputation for trying to stem free speech and the flow of information about what is really going on kind of makes sense.
The blog post also makes mention of traffic being disrupted a couple of times on varying scales before this major outage occurred which kind of signals that they were testing bringing the whole Internet down beforehand.
Kind of muddles up why and how, but it's quite clear that someone made a call to the state ISP, and then someone went around reconfiguring the routers to drop all the published routes into Syria.
From the article: "our network team estimates that Syria likely has a small number of edge routers." I'd imagine it was an easy to implement given the appropriate access.
I'd say that's more unlikely. It's just a lot easier to sit at your desk and issue a couple of commands, which will guarantee getting the job done. Unplugging things is messy and unreliable in contrast, with redundant links, rings, and who knows what.
They have previously been used by Egypt to close down their internet. I have no insight into how this particular incident was accomplished, but this sort of software is where I'd start looking.
At one point when I was looking to see what was available in the job market, I saw a posting that I was a suitable fit for with their organization (netsweeper). It got me curious, being tangentially aware of their organization and content filtering focus. Their perspective was very contrary to my own, and I was interested in having the opportunity to have them pitch what they did to me. I hadn't really had the chance to talk face to face with what I considered to be an "evil" organization before. Maybe it was unethical for me to waste their time, when I didn't have the intention of working for them, I don't know.
The interview itself was interesting. The technical tests etc were relatively trivial, mostly stuff you'd expect about load balancing and responsiveness (as would be required for routing software). But more than half of the interview was them pitching the company to me -- they're quite aware of the reservations people might have about working for a company whose direction is to suppress free speech.
Their basic pitch was that they believed all 1st world governments would have internet filtering technologies in place in the near future -- that governments would legislate the use of it to stop the proliferation of things like child pornography, and eliminate the zombie-computer defence -- that if there were child porn on your computer, you went and got it.
We talked a little about the technical challenges of instantly shutting down the internet of an entire country, like Egypt, but they more or less blamed that on "improper configuration" of settings. At one point in the interview, the interviewer told me that you have to believe that the people that make the weapons aren't the ones firing the guns, and that dangerous tools can be used for good, but that yes, there were nights in which he cried himself to sleep.
Maybe it doesn't tell us directly and the title is a bit strong, but so is the word 'nothing'. Cloudflare tells us quite a lot. It is unlikely the terrorists cut all the lines, so that is out. That is information I didn't have before this blog post.
That leaves a few options of how to shut off the internet of a country, and they give a pretty plausible one, and who would have the authority/power to do it. And they back it all up with evidence.
There's some guesses in here, but the title is rather misleading. No one still knows why these routes are no longer being advertised, only that they're not.