The first thing that came to my mind after reading this was that one should not talk about his crypto investments with strangers or friends as it can pose various risks. If you are active on forums like bitcointalk and involved in trades, you should not give information which can help others relate to your identity.
Partying together. I guess he accidentally spit out his investments, or his crypto-related business. Another one is that, one of the captors already has a past crime record. He trusted the wrong people I guess.
Now with regards to sharing sensitive information here, I've been in the forum for quite some time already, and I didn't shared any personal information or trades, or anything that might affect my privacy here. I mean why would you share personal information here in a platform where you don't know any user personally. I guess a gullible newbie who can easily get tricked is the one that might do it, but for those who've been in the crypto for a long time, they know that sharing information here is a no-no.
For me, I have told to some of my relatives that I'm holding some cryptocurrencies, but I never told them the total amount that I have. I just feel very uncomfortable to share with them the total portfolio that I got, and I guess just telling which coins are you holding is good already. For those who are holding huge amounts of cryptocurrencies, or even just a small amount, don't ever share it to other people because it might be a reason for them to make something bad to you like what the captors did to the investor in the article the OP shared.