At first I thought they were hunting down everyone who "wasn't supposed to be there", then they said Deke didn't quite match, so clearly they aren't used to variation in their readings. However, that would also imply they have never come across anyone who was an outlier, but not a correct target before, which seems unlikely. I assume Daisy would register oddly since she has superpowers. So I'm still not 100% that they are only looking for parasites.