I'll give you the benefit of the doubt that you're not stupid or trying to troll.
Introverts' social batteries recharge when alone (generalising).
The joke is that they're in the cool-down period.
It really isn't very complicated.

If you still don't get it and are an extrovert, imagine how you'd feel when forced to be alone (by your friends, of all people) - which is a mirror of forcing the opposite to socialise.