What does "He heard his voice go high and fast" suggest about Arjun?

Arjun had spent his last ten rupees on a samosa at Nashik station, and only when the train began to move did he remember that his ticket was in his brother's bag, and his brother was in the next coach.

He sat very still. Every time the connecting door opened, his heart jumped. After an hour, it opened for the ticket checker: a tall man with a grey moustache and a notebook.

"Ticket?"

Arjun explained. He heard his voice go high and fast. The man listened without a word, then wrote something in his notebook.

"Your brother's name?"

"Rohan. Rohan Deshpande. Coach S4, I think."

The checker walked off. Arjun sat for twenty long minutes, sure he would be put off at the next station. Then the door opened, and Rohan came through it, grinning, with the ticket in his hand. Behind him came the checker.

"Next time," said the checker, "keep your own ticket in your own pocket." He punched it, handed it back, and moved on down the coach.

"He came and found me," Rohan said. "He walked through three coaches calling our name."

Arjun looked down the aisle. The checker was bent over another passenger's ticket, as if nothing had happened. He had not smiled once, and Arjun realised that he had not needed to.