Hmm, reading the bet again:
"as little as 10% of current-generation ASICs" is marketing speak for "10% (rounded down) of the least efficient ASIC you might have been able to buy on the day we wrote this"
"Current-generation ASICs is defined as 1W for 1Ghash" is the bet maker only considering the most efficient ASIC he could find: Bitfury @ 0.9 J/GH
Then proceed to take 10% of 1 J/GH times 400 GH and you get 40W.