That's not completely accurate either. The pheru didn't just have abnormalities, they where changing. Humans who ate the infected ones became infected themselves yes however the abnormal growths where early stages of flood transformation. The "powder" that humans discovered was more than likely spores broken down. The growths if you think about it where like the parts of a infection form starting to form. The pheru where herbivores however after being given the powder they began forming growths and eating each other. The flood can infect and control anything with a complex enough neural network. It's a possible that the flood merely accelerated once they infected a more complex and intelligent species.