@Kanol But that's exactly the point of using a historical basis, like yourself admitted, the author is using a historical model, so why would it be weird? We have the trappings of roughly medieval society, with the work showing customs and thought process associated with that time frame, such as arranged marriages, noble privilege, etc.
but someone could just as easily take deadly offense over someone not spinning counter-clockwise after blinking in their presence or something.
But that's not what the chapter showed us. The knight reacts to Sera being startled with, "You're being rude to Sera-sama." and drawing her sword, and when Satou puts his arm around Sera's waist, that's when she reacts with "You insolent cur!" and goes to strike him. Both of her reactions indicate that the problem lies with impropriety towards Sera, who was established in the previous chapter as someone extremely important to the Tenion Temple and the dukedom for that matter, beyond what the importance given to a normal oracle priestess, as shown previously when oracle priestesses were introduced.
In addition, the author and artist have shown information that Japanese culture has come into and influenced this world at various times, either through reincarnation or hero summoning, such as the Saga empire's hero, the pottery glaze notes, the ancient, giant tori gates, and even the first king of the ancient civilization called himself "Yamato", an archaic way of referencing Japan, being that it's the clan name of the Imperial family. Along with the fact that this work being aimed at a Japanese audience, a culture with proper respect so ingrained that two separate forms of speech exist for conversation.
So with all this background and world building shown throughout various past chapters, to establish the setting as a medieval fantasy world with similarities with real world historical time periods that's further had Japanese cultural influence at various points in time, possibly even from the Heian and older time periods, that would justify the knight's reaction to a "disgraceful" action to her mistress, you want to claim that as a logical fallacy?
Also in context it seems weird to escalate to violence that quickly unless you know the person of position you're escorting is cool with you cutting down kids for minor perceived sleights. Someone who's expressed a lot of interest in the welfare of orphans recent is probably not cool with it.
Except again, they're not just kids, they're beastkin. Or demi humans, ear-kin, whatever the translation group picks. The previous chapters already established that discrimination and persecution against beast kin was normal in this world. The majority are enslaved, and the ones not are viewed as savage thieves and bandits. Remember that Pochi, Tama, and Liz were basically setup to be stoned to death by the priest of Zycuuon temple. And when given the option to be freed, they begged to stay as slaves cause of how bad the persecution was.
Now Sera may care for children, but it's not established how she feels about beastkin. Her surprise at seeing Pochi and Tama were beastkin could indicate that she has the same prejudices...or not. Likely we'll see it next chapter or so. But from what we have seen about this world, it should not be surprising at all to have Pochi and Tama get cut down because of "perceived sleights", and Sera only feeling a little "sad" about it.