I guess similar to how Rick and crew smeared themselves with walker guts to blend in with and escape large crowds of walkers. I guess the Whisperers take it a step further blending in with the masks and guiding the mindless herds in the direction they want.This fight with the Whisperers is one that the group would be better served to avoid. As illogical as it seems, they have the full power to manipulate herds of walkers and use them as camouflage. How is that possible!?
My bigger question is how the heck did Ezekiel not smell that Alpha wasn't from Alexandria or Hill Top. I feel that Alexandrians and Hill Topians would have some sort of hygiene materials to keep clean. Alpha, who roams with the dead, would have to smell like pure trash and a--. Especially when she got close to Ezekial and blew her breath in his face. lol