A large part of Castiel was actually touched that Ben was trying to warn him of Ruby's supposed infidelity. But the truth was the relationship between Ruby and Sam was much more complex than that, in ways that Castiel didn't even know, which did concern him more than he liked to admit.
"Yes, Ruby knows stuff, but I happen to know more," for a brief moment there was a very unangelic grin on Castiel's face before he became more serious again.
"Alright, how much do you know about what makes your uncle special? About his powers?" The last thing Castiel wanted to do was drop some bombshell on Ben about the demon blood from Azazel and what it meant for many demons. But at the same time he wanted to be honest with the boy who had, in his way, tried so hard to help him.