Even if the statement "Human Beards contain more bacteria, especially human pathogenic strains, than dogs' fur" is explicitly true, that statement would only really mean "dirtier" in that specific context. Of course humans are going to have more human pathogenic strains than dogs, because humans are the desired target for those bacteria. This might tell us that it could be safe for human patients to follow up in an MRI that has been used on a dog (the stated goal of the study), but if we want to actually determine how dirty beards are by bacteria count we should compare them to human mouths, hands, and mobile phones.