Nah, they've been quite rash before. A couple of months ago both Terran and Aurvandil sensed that the other was weak, and so optimistically they launched subsequent invasions against one another, despite neither of them being fully prepared to launch said invasions. Predictably they both failed in embarrassing displays of incompetence.
The push into Chesland was likely inspired by the fact that it had gone rogue, and thus the defenders couldn't make use of it's walls and there was potential for Aurvandil to delay the takeover and mop up another tid bit of Terran's military at the same time.
