So let’s assume it was the Cishaurim.
That would mean Moe was the author of the attack.
I don't think so?
Xerius was ready to impose the Imperial Saik onto the Holy War via Indenture. Moenghus didn't need to instigate the Scarlet Spires to have a school for Kellhus or the Holy War. Furthermore, if his intention was to convince a school to join the Holy War, he could have somehow manipulated the Mandate into pursuing new Consult Spies to Shimeh when Maithanet declared the Holy War (that actually would have made an incredible read, had the X-Factor of the Dunyain not always being a crucial part of Bakker's plan) (hell, reasons Moenghus didn't do this may even feed into reasons for a party other than the Cishaurim crashing the Scarlet Spires' Sanctums).
Also, there is the discrepancy between Aurang's reminiscence and Kellhus' retelling of his father's narrative, "decades" vs. "twelve years," which casts doubt on the narrative entire.
I happen to believe Kellhus is right about the narrative, excepting the years. But then there's lockesnow's skull to consider, "Kellhus' mis-step" literally following his narration of the Scarlet Spires' attack.
I can't imagine it was the skin-spy anomaly, only because I think the ability to work the Psukhe requires a real (as opposed to Consult created) soul.