What does Kabir mean by "You saw"?

The ball went higher than any of them had ever hit it, over the neem tree, over Sharma-ji's wall, and through his kitchen window with a crash that stopped the game at once.

For a second nobody moved. Then eight boys discovered that they all had somewhere urgent to be. Within a minute the lane was empty except for Kabir, who had hit the ball, and his little sister Tara, who had been watching from the steps.

"Run," she whispered. "Nobody saw."

"You saw," said Kabir.

He walked to Sharma-ji's gate and rang the bell. His heart was beating so hard he was sure the old man could hear it. Sharma-ji came out holding the ball in one hand and a piece of glass in the other, and looked at him for a long time.

"I hit it," Kabir said. "I'll pay for the glass. It might take a few months."

Sharma-ji turned the ball over in his fingers. "Thirty years I have lived in this lane," he said at last, "and every summer at least one window. You are the first to ring the bell." He handed back the ball. "Pay for half. The other half is for ringing."