Was the Red Hood assuming or did he know that Batman had been out of town? And if so, was he keeping track of general reasons or personal reasons? Damian also found in interesting that the Red Hood hadn't committed himself either way. Presumably talking to Batman was an option for him.
Curious. Ties to Batman... a familiarity with the League of Assassins...
"I'm the newest Robin." Damian said in a tone which pretty much implied that the Red Hood was unable able to see the obvious. His body language, however, was clearly challenging, best interpreted as 'and what are you going to do about it?'