Re the highlighted part: I think it's unlikely that even the Keystone Cops in this case literally poured Luminol solution onto the floor. But I do, however, think it's highly possible that they sprayed so much Luminol onto certain areas that they effectively ended up creating pools of the solution. Of course, the proper procedure is to apply a light mist of Luminol to the area being tested, in order to preserve the shape and integrity of any evidence to be exposed.
And regarding the strange sensitivity of the Luminol photos produced in this case, I strongly suspect that the exposures on these photos was pushed - either deliberately or through incompetence - and had the effect of maximising artifacts and the tiniest of reactions. We already know that the "official" exposure settings for many of the photos was 2-3 times higher than the recommended exposures, and there also may have been digital balance/contrast alteration applied (just like, for example, it's possible to do with photos of the walls of the cottage at nighttime

)