Q. I assume the answer (on question 2138 that "dry flour that did not come in contact with water Poskim are lenient" and permit its inclusion in the chometz sale). is referring specifically to flour of which the grains were moistened or washed before grinding, because if the flour was ground from grains which were always dry, it shouldn't even be a leniency.
A. The above refers to the common unsupervised flour readily and ordinarily available in the market place. Although sold as always being dry, those source grains could have been made wet after harvesting by the rain in the field, or the condensation, leaking, washing etc. during storage and grinding. Therefore, the leniency for sale is required.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit'a
The standard practice for commercially available flour is that, following mechanical cleaning of the grain, the wheat is moistened and allowed to rest while damp - this makes the bran tougher which allows it to be more completely separated from the endosperm when milled. Thus, the presumption should be that all flour purchased for home use is chometz gamur.