Not having heard of them is understandable, I hadn't either, but the reason people have been downvoting you is that it took you longer to write out that comment than it would have taken to do a quick google and see there's a wikipedia page that starts with "SonicWall is an American cybersecurity company that sells a range of Internet appliances primarily directed at content control and network security."
But @sambazi's comment talks about ISPs doing the blocking.
Yes of course, internet appliances are capable of DNS-blocking whatever their operators tell them to block. This is not news to me, nor to anybody else reading Hacker News.
Also the vendor of this appliance does not classify things as "Extremism". The owner/operator of the appliance does those things. Claiming that "SonicWall is classifying it as Extremism" is like claiming that "Intel marked your email as spam" because your SMTP server uses an Intel CPU.
the point is that most isp's use 3rd party blocklists (sometimes by government mandate) and chedabob gave a source of one popular vendor doing just that
I was suggesting it had been incorrectly classified previously by a single vendor, presumably in response to a report (or a court order) for a single page. There's no nuance to the filtering, so the whole site gets blocked.
It happens regularly for Imgur: Someone posts CSAM, and the whole site gets added to Cleanfeed (the UK ISP level filter) for a couple of hours until the original image is removed.
also: source?