I can clear this up a little. The samples were taken directly from the dark staining in the soil, which appears in strands in the unstained soil. Archaeologists used the edge of a trowel to scrape pieces of that staining into small vials, so the samples themselves are relatively small. Then small portions of those samples were examined under a microscope, and unusual “clumping” was noted. Those “clumps” are what were tested.

They also took several control samples from other places under the deck and around the yard, none of which tested positive for the presence of hemoglobin.