If Lei Chen had only plainly showed the Zephyr Academy polite concern, it would not have been a big issue. But Lei Chen had first sent his guards to inform the Dragon Slayers Academy but the Zephyr Academy had unashamedly cut in and invited him over instead. Although the Dragon Slayers Academy did not really place that much importance on gaining Lei Chen's favour, but having been slapped publicly like that was not something they were prepared to take lying down.
They did not mind who Lei Chen chose to be friendly with, but if they were humiliated by others, they made sure they seeked recompense.