Disclaimer: just an opinion of someone on the web, it's not health advice. And I might be wrong.
With that said...
In my opinion it's wrong. He can't control his ANS just by using his mind. He uses: breathing techniques, exposure to cold and having the right mindset in order to withstand the cold. There's also a Dutch article on the site that says this. The way he handles the cold is also the same way he handles his ANS in general.
I think the wikipedia page is wrong about it. Also, the researchers that did studies on him at the Radboud University of Nijmegen are not specialized in understanding meditation. In most cases I'd disagree that what Wim does is meditation at all. While I respect the knowledge of the researchers, I think they were dead wrong in understanding what meditation is back then. It's really more of a behavioural thing with your breath. The meditation I know is more about mentally focusing on your breath or body, not physically altering it. Their expertise is in all sorts of: viruses, bacteria and the human body in general -- including combining the 3 for experiments.
Here is a better source about the science of Wim Hof: http://www.icemanwimhof.com/science
In my opinion that source is a lot better. Then again, it is a very wise to be sceptic (hint: also with my post). I think a lot of people made wrong claims about his method. I think almost everyone involved made at least a wrong claim about something of it. People are enthusiastic and lack expertise in some area and that's when claims might be overstated or misinterpreted by the one reading about them.
You don't have to be too sceptic though, it definitely works and improved my life. I love all weather now with regards to temperature. I sometimes use his method as a natural painkiller as it releases adrenaline, though I'm still on the experimental side with that.
The reason I believe to know all this is because:
- I participated in one of the experiment and trained for 4 days with Wim and other participants
- I asked a ton of questions to the researchers who were there from the Radboud University.
- I have 400 hours of meditation experience and read about 100 articles on them from Science Daily, and about 30 real papers and 1 book about meditation that uses science as its way of justification (Search Inside Yourself by Chade Meng-Tan).