Splinter is angry, yes. But it is only a momentary angry, and not one that will fester for a long time. They were stupid, but hormones were partially to blame. A cold comfort, really--except that Robert didn't know him well enough to tell the difference.

"I believe I remember wishing for you two to be discreet," Splinter states, making sure to pronounce every word. "For neither of you are ready."