[RCW1945]

This is supposition but it fits the observed incidents.
Siavash observed, in very general terms, that K&K were criticising Noirin for not joining a (their) group. He also saw K and Sophie pretending to be rabbits (or dinosaurs, it doesn't matter which).
When he reported this to Noirin he combined the two to give the notorious phrase "hopping from group to group like a rabbit".
For some inexplicable reason Noirin seemed to find the "rabbit" part particularly insulting and blew up.
When K&K were accused of using the dreadful phrase they could easily deny it because, although they had often expressed the sentiments, they had not used the unholy insult of calling Noirin a rabbit.
So how does that sound to you?