First off, he [Guilty Spark] calls the little popcorn Flood "rangers [which] carry spores" This alone should've alarmed people before- Guilty Spark is hinting that the "rangers" aren't the basic form of the Flood- rather the Flood has no basic form, it is a disease, a virus, a contact based spore infection. Perhaps over the years of Halo, however, the experiments that needed performing required the Flood to have a host- and over time, this host became an integrated part of the Flood (like mitochondria for us.) What these "rangers" were in their uninfected form remains to be seen.
Commence investigations.