You're right. A buy at .42 earlier in the day would not make the price drop, especially when it represented so much of the volume of the day.
Had it been appropriately represented during the day as it took place, IMO we wouldn't have seen a price decrease but rather a price increase over the day. 370,000 shares is immense price support especially since they were all likely at the ask rather than the bid and likely at late morning when both the bid and ask were in that range.
I like this stock, but I'm now stop-lossed out and waiting for a new entry level when the gold dust settles.