It means they are less stressed than the fish who actually have it, thus the more stressed fish are a more suitable host for the parasite.
Slime coat production is based off of two things, it can either be stimulated to grow via a hormone or waterborne irritant.It is produced by specialized cells scattered through the epidermis. Just as a little piece of info, that is actually how aquarium salt "boosts slime coat." Since it has no know hormonal properties, it actually stresses the fish to improve it.
As for their thoughts to their owners, there still seems to be no evidence that fish can exhibit complex emotions. They still seem to have very wild instincts, driven by their stomachs. My fish do react to certain things, like me walking up to the tank, me opening and closing the tank stand, etc. because they know that results in food. However there doesn't seem to be any other bond between the fish and the fishkeeper. Some people "pet" larger fish such as Oscars, however that is more for the sake of the person, to feel like they are bonding more with their fish.