I can't answer for the poster you quotes, but for my own part, it's not a fear or inadequacy, it's a preference.
I don't enjoy liver. I've tried it. I know I don't like it. I don't need to "get over" my dislike of it. I need to avoid it.
The older I get, the less I want to mix. Or, the choosier I get about with whom I will spend my time/energy.
To me, small talk or making an effort to socialize with strangers is work. I can do it when called for, but it takes energy. I usually don't find the conversation to be enriching enough to have been worth the energy or attention. Meals are relatively long occasions--this isn't a 5 minute chat before we get on Soarin'. This is 30-60 minutes of keeping the conversation going.
Even if they're perfectly nice people, smiling and nodding and learning they're from Memphis usually doesn't add enough to my life to make it worth sacrificing a meal enjoying the company of my family, friends, or even the peace of my own thoughts.