Well, I was playing devil's advocate to some extent there, I am 'guilty' of lots of seemingly random interests too (in several cases with certifications that took years to acquire), and even multiple academic degrees in 'hard' subjects. It's just that I don't necessarily put all of it on my CV (the hobbies, the degrees I feel I have to list, even though less would probably be more there too), especially if it's been a while since I last practiced them.
The scuba example was on purpose, because if you list credentials for things that you aren't actually proficient in, it shows something else about your attitude towards being honest about your skills (which can be crucial in technical roles). At one of my old employers, my later boss warned me that the last interview round with a very senior guy was mostly a formality, as long as I'd been honest on my CV. He liked to grill people a bit about their inner workings and their journey, and he'd famously once rejected the team's top choice because the guy had claimed to be fluent in a particular (natural) language on his CV, and then turned out to be anything but (that language was of course in no way needed for the job). In situations like that you feel vindicated if you've had a think about whether old credentials that you acquired a long time ago realistically still belong on your CV. Skills that you don't practice can be lost, regardless of what some paper says.
But if you are serious about them, then by all means put your hobbies on your CV. It can lead to great conversations sometimes, and it's also a form of honesty. And yeah, sometimes people will read things into it that are beyond your control (if you're a pilot, those will mostly be positive, if you do MMA, they may be more mixed, but I'd argue you should mention it regardless).