I don't believe much of what is said on the internet about the Strid. It's not a magical river. The Strid is dangerous, but it acquired that reputation by killing unprepared people who fall in. I've not seen much to indicate it's especially deadly to helmet and PFD equipped paddlers.

It's possible that the man depicted could have been dragged under an undercut if he'd swum the full rapids, but the video doesn't show evidence of that. Rather, he's pulled out of an eddy without much drama.