It is from Crash Course Media Literacy. It is at 4 minute and 52 second. Here is the context:
Suddenly, anyone, even an unlikely street kid without two pennies to rub together, could be in the know and feel like they were the king of the world.
I am aware of what the adjective means, but I cannot get what it means there. Dictionaries say that improbable is a synonim to unlikely. How could a kid be unlikely or improbable?