Except more money... Assuming that he assumed it wouldn't backfire like it did and maybe hurt sales. I never saw a pricing error on Steam during a sale that lasted anywhere near that long. The longest has always been around 30 to maybe 40 minutes. Five hours makes an accident seem incredibly implausible.
Things happen. If he was at an event and still in the mindset of the game being 50% off instead of 75% off, he probably didn't even think about it until finishing up what he was doing. It's just as plausible as OMG CONSPIRACY.