Cassian had spent most of the time in a chair by Kay-tu's bed while his friend had been in his 'coma'. Sure most people said there wasn't anything to worry about and that the former droid would eventually wake, but Cassian was determined to be there for his friend.
He'd had to listen to him die on Scarif, stuck behind a vault door unable to help. If he'd tried to help he and Jyn would have died too, and the death star plans would never have gotten to the Alliance and all their deaths would have been for nothing. The mission had to come first. That wasn't the case here.
So he'd been there, reading and thinking, sometimes talking to Jyn if she sat with him. And of course the former droid would wake up when he stepped out to fix something to eat. That bellow had never sounded sweeter.
He was back in the room in a flash, his expression giving no hint of the past worry and now relief that his friend was awake again. "You bellowed?"