Or someone got the report a few hours early, didn't want to be seen to jump the gun (insider trading, and all that) and kicked off a new trading strategy 400ms earlier than they intended...
Which begs the question of whether it was accidentally early. It may well be that the 'early' trader knew they weren't the only one with early access to the data and intentionally set their trades to be a tiny bit early, to increase their chances of getting out ahead of the people who schedule their trades for just-after the scheduled announcement. Which may well indicate a larger problem than one guy with a tip.
I mean, I know that traders are probably pretty anal about accurate clocks, but mistakes do happen.