I don't know if you're a techie or a businessman but my feedback is almost the same either way. The people you describe are
usually quiet / shy -- or simply don't throw themselves at people's faces, which is something very different.
I am the latter type; if you hit me with an interesting topic, I can talk with you for hours and will very rarely repeat myself (how valuable what I am saying for you is of course strongly dependent on your interests). But I won't come to you trying to catch a conversation about what I find interesting. I'd be much more likely approaching you with a generic opener and try and find what you do find worth talking about. Anyway, here's what I believe is a good approach to the people who do things in private but [almost] don't network (like myself):
- Don't assume quiet people are not interesting. EVER. My wife is easily the most intelligent human being I've ever met and I've had to work a lot during our first year in the relationship until she started openly sharing what she thinks about this or that. And then I found myself having my mind blown by very different perspectives, many times, consistently, to this day (we're about to have a third anniversary very soon). Some people are not amazing at striking a conversation but if you manage to engage them, you might discover a treasure.
- Show genuine interest in what the person is doing at the event you both find yourself meeting at. I'd be very honest with you and one good example of that honesty would be: "I believe I spent so much time perfecting my engineering skills, and now I simply want to listen what people need from technology; how do they want their lives improved by it". That would probably open a plethora of possible follow-up topics.
- Many of the people of my type find networking and investing in a portfolio / GitHub profile / LinkedIn profile / general reputation a low priority activity. That's of course horribly misguided since millions of years of social instincts can't be overriden but there you go; I am 37 and only now I started actually understanding the value of these, and started slowly working on them. That's the thing: I've been busy with far too many other things to even consider networking for so long. Food for thought IMO; strike a conversation accentuating what the person is thinking and doing now, not what he/she was doing all their life up to this point. The past can wait for a later convo.
- Finally, as the article suggested, do offer some value to the conversation even if you find yourself getting a lot of important information for free. I am a bad salesman of information and I'd tell you a lot of things we the programmers do without telling our bosses (one random example; another one would be some trade secrets) but if 15 minutes later I realize that you haven't offered a single interesting piece of info or a compelling question, I'll politely excuse myself and will go look for another person to chat with.
Hope that helps a bit.