But Peter often does act childishly. He is consistently reactive and impulsive. Two or three episodes earlier, he ran off across the country and actually made a point of not telling Walter or Olivia where he was.
Ironically, because they hadn't treated him like adult, who can make his own decisions. I actually don't blame Peter for running at all. It'd have become a very different show, (obviously), if he'd stuck around and given Walter and Olivia the lumps they completely deserved.