H5N1 isn't exclusively avian flu, and the current receptors for the strain circulating in the U.S. have much more affinity for binding sites found in human eyes

H5N1 isn't exclusively avian flu, and the current receptors for the strain circulating in the U.S. have much more affinity for binding sites found in human eyes (hence conjunctivitis being one of the most common symptoms) and bovine mammary tissue. "H5N1" is a crude description of a wide variety of strains, some more amenable to avian hosts, some not. As for why milk is being dumped into the wastewater system? Because that's where it goes.