Why would unprofitable mining cause a upward pressure on price? There is a fixed amount of bitcoin distributed per day cumulatively to all miners regardless of their number.
I doubt the recent price drop is due to people buying and selling in bitcoin since it's way too steep a decline.
I'm guessing that most miners themselves also happen to be investors as well. After all, if you believe in bitcoin enough to purchase equipment to mine it, you must also believe that the price will at least stay constant or rise. So it seems natural to keep some of your profits in bitcoin.
So people mining and investing together are heavily dependent on price, more than those doing one or the other. With the constant slow decline, it left a lot of miners languishing, and they not only need to convert all their current profits to their local currency to pay the bills, but their bitcoin investments as well. This creates a feedback loop and an ever increasing rate of price decline until enough miners run out of bitcoin to sell and/or close up shop.