I concur with what you say, but rather than social threat, I think of it as over-stimulation and sensory overload. Rather than being socially introverted, to me the challenge is dealing with the sounds, visuals, distractions and general chaos of most social situations. It feels more like having a tennis ball cannon aimed at ones head rather than having to keep ones guard up and shield oneself against others.

Sounds like there are different ways to define or come across as introverted. I attribute my disposition more to sensory sensitivity reminiscent of autistic or ADHD-like traits rather than social anxiety.