Sirius probably could have thought this through a little more. He'd mostly been focused on getting to the house, but having to deal with someone hadn't completely entered into the equation. Considering he'd been gone for so long, he didn't know who still knew him, or of him at least (in a favorable light).

"As a matter of fact, yes," Sirius replies. "I guess you could say I'm here to renew my membership."

No other choice but to dive right in really.