The only thing Ansom didn't know was that the center hex was empty. He knew all about the other stacks in the fort.
And he came anyway. Meaning he evaluates his chances to survive attacks by all the dwagons in the fort to be very good -otherwise it would have been a real suicide, center hex or not.
I belive Lord Hamster wanted to take the "sente" and lead the fight. He knew ansom was powerful enough not to fear the dwagon formation, so he lured him inside the pincher, knowing he would not fear to be inside it. Now Ansom is far from his own troops, gained nothing, has no move left - and the dwagons can go away without fighting if the uncroaked lords catch them on their way.
I suspect Ansom won't be attacked. The next fights will be far from his hex, on units that he would have protected if he had not thought he could kill all the enemy warlods at once.