Maybe they changed their mind about that halfway through (and they were particularly resistant to the sunk cost effect). I agree that's not very likely, though (probability < 10%).
(BTW, the emphasis looks random to me. I'm not a native speaker, but if I was saying that sentence aloud in that context, the words I'd stress definitely mostly wouldn't be those ones.)
Thanks for the feedback on the bold formatting! It was supposed to highlight keywords, sort of a TL;DR. But as that is not clear, I shall state it explicitly.
Update 2013-09-05.
I have since played two more AI box experiments after this one, winning both.
Update 2013-12-30:
I have lost two more AI box experiments, and won two more. Current Record is 3 Wins, 3 Losses.