What would be your basis for not ruling that out?
That this is not a regular price mistake where the item is listed incorrectly and you can claim ignorance. Rather, you had to jump through a series of hoops to get the price reduces to zero. On top of that, it's not as if you placed a large order with a couple of these free items thrown in, but rather placed large orders of only the free products. I would think that in light of the preceding, there is sufficient evidence to demonstrate an intent to defraud.