Those numbers are old, aren't they?. The console usage rate has been falling since 2011 when it was over 60%, and is likely well under 40% now (see for instance http://www.forbes.com/sites/insertcoin/2014/10/03/netflix-usage-on-playstation-xbox-is-declining/#66feba427167).
People who own a smart TV are likely to use that for Netflix, rather than a console. People who own 8th gen consoles are more likely to own smart TVs. Combined with the adoption rate dropping, it's reasonable to assume that a large chunk of the people who use Netflix on consoles use it on older consoles.
Last gen, 270 million home consoles were sold, while just shy of 90 million have been sold this gen. So you've got somewhere around twice as many people who own a 7th gen console but not an 8th gen one, as who own an 8th gen one. If we make the simplistic assumption that each customer is equally likely to use netflix, no matter which console they have, we can get some numbers for usage. Total numbers for consoles are a bit shy of 40 million, so 7th gen would be around 25 million, and Ps4 just shy of 10 million.
I'm not sure why you find that to be a shockingly large number, though. Somewhere around a quarter of console owners use it to also watch television. If anything, I'd say that's lower than I'd expected.