Normally I would agree. But sometimes it's not that simple. Our last dog was terrified of old ladies. My mom said they had a dog as a kid that was afraid of my grandfather if he wore a hard hat. My paternal grandparent's dog wouldn't come near my grandmother after she had heart surgery because she smelled different.
That is true while in many circumstances when an animal fears something it can usually be a sign that person is of questionable purposes there are times an animal will fear due to either past trauma as in the case of animal abuse or just plainly they fear that person due to lack of trust or their appearance is one that intimidates them due to a variety of reasons that often times can be hard to comprehend.(⊙…⊙ )
Animals are complex Σ(  ̄□ ̄||)creatures so while some may avoid people out of fear others will and may avoid them due to their natural instincts warning them of the possible threat. ヾ(☆▽☆)So yeah I do agree with you(๑•ㅂ•)و✧ when it concerns animals it is not so simple. However in this story I would not at ALL be surprised if it turns out the reason the dragons fear both of those two is due to the dragon's instinct in sensing the danger the "fiance" and her hunter do and or are liable to bring. ヽ(`Д´)ノ ( ̄へ ̄)
My cat does that with this one mask, fur all haunched up as she hisses up a storm looking like a raccoon. It's either instincts or a underlying trigger in the mind. Just as no person is alike it is the same for creatures.
As for emotions, those can trigger different effects in animals. My cat [yes the same one that is afraid of a mask] is a emotional support animal so she's very attuned to emotions. If someone is experiencing a darker emotion say stress, depression, anger, ect she'll respond depending on the amount of the negative. If it's not too heavy she'll work her way to trying to calm you however if it's heavier then she can help she will respond by crying. If the heaviness continues she becomes affected and in response shows your negative emotions her way to make you realize you've done fallen deep.
Animals are intelligent, they may not know how to speak to us, but they try to communicate. Those dragons are trying to give the hint that those two are "no good" while Queen would stay to kill them because she must protect her bonded knight so she can't just leave him. Similar to an service animal be it medical, therapy, or special needs they all respond to triggers.
Some animals may lack the knowledge to what others express an emotion to. It might be their first experience so they may not know how to express it, but in all mythologies dragons are know for their high intelligence so for them to act this way is actually normal and common to put into thought. Why mess with something you can just avoid altogether? Could be this 'scent' or 'aura' or even 'feeling' of what is negative that makes their instincts say flee. Kind of like how you said the dog avoided your grandmother after she had heart surgery, scents are very important to dogs. That is how they remember their "important" ones, be it another animal, a flower, a toy, a location, and of course people. When someone's scent changes in the snap they become labeled "stranger" since the scent they have isn't the scent in the dog's memory. The older a dog gets the harder it is for them to remember new scents. Sort of on the same line as someone with a mental deteriorating disease.
Anyways that's my two cents.
Animal really sensitive to bad intention people, so if you are being hated by an animal, it must meant you are a bad person!!!