It is to express approval in a cool ass gangsta way.
Similar to "That's RIGHT Bitch!"
Guy 1: "I wake up the birds. The birds don't wake me up"
Guy 2: "Downstreet!"
It's the small town word for downtown...when downtown consist of one main street...and that about sums up the shopping district...
"I'm going downstreet to meet some friends for a day of shopping and tea!"