Is that the Strid? They don't say the name of the location in the video or in the description. It also looks a bit different to me than the pictures and videos of the Strid.
I'm no whitewater expert, but this doesn't look like a near drowning to me. He probably attempts to roll but is obstructed by the rock and current, then exits just as assistance arrives. The hydraulic is potentially dangerous, but most of the circulation he's stuck in looks to be horizontal, and I don't see reason to think he couldn't have swum out if need be.
Not according to all the information discussed in the other comments.
> most of the circulation he's stuck in looks to be horizontal
This section has up to 60m depth, the underwater currents are extremely turbulent and will you pull you under the rock on the sides (the whitewater is just a 'slit' on the surface, there's a whole river running underneath). If he didn't have someone ready to pull him out in two seconds like in the video, it's a good bet he wouldn't make it out.
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.
In a river, they're called strainers. If someone is caught against one, water pressure often makes it impossible to extricate themselves without assistance, and if their head is underwater when they become trapped, rescue may not come quickly enough.
They're also less predictable than a lot of other river hazards. It's possible to come around the bend and be faced with a big strainer that wasn't there the last time you ran the river.
