Somewhere in the fandoms

First, both Arrax and Luke were really young and had absolutely zero combat experience. As soon as they saw Vhagar, it’s very obvious they simultaneously became a lot more tense. Then after Luke had his encounter with Aemond and left you can see Arrax looking in the direction of where Vhagar was in clear distress and Luke does the same thing before mounting. Luke realized their anxiety was high and he did his best to calm Arrax down before taking flight, but that all went out the window as soon as Vhagar gave chase. Now you have a child and a very young and small dragon that are bonded together in a very scary situation: being chased down by a behemoth in the middle of a raging storm (poor Arrax was flapping his wings as hard as he could) I personally think Arrax went on the offense to try and protect both himself and Luke, if only to give them a chance to escape. Both of them did the best they could.

Then you have Vhagar, an extremely old, massive, experienced dragon that is bonded to an inexperienced rider who is feeling a lot of unhinged rage and resentment. They were flying in attack maneuvers ffs I doubt she thought it was a game. And then this little dragon has the audacity to breathe fire in her face. Of course she’s not going to deal with that shit, as utterly tragic as her response is.