I think it's mostly that introversion vs extroversion are closer to what the post you are responding to, while more often then not, social anxiety and shyness are conflated with introversion while that is not necessarily correct. Introverts exist that are comfortable interacting with groups of people. Being "drained" by social interaction doesn't mean that they don't enjoy it or that the draining is stressful. I think of it like a timer that counts down until you'd prefer not to be in social situations anymore.

That being said, I consider myself extroverted and I experience an opposite effect. After being in non-social situations for a long enough point I get to where I don't care what specifically I'm doing I just want to do something social. After a day of reading or individual pursuits I might feel a little stir crazy and text anybody I know to do anything from go get a bite to eat or hang out with no particular activity in mind.