Given that the corruption in the Savalirwood, which originated from the Ruins of Molaesmyr, is present in the ruins of Aeor, new theory:
This is all tied to Ludinus Da’leth.
Da’leth, much like Vess DaRogna, is extremely interested in recovering and using magic and magical tools from the Age of Arcanum that are found in the ruins of Aeor. We know this because the Mighty Nein just found the dead body of one of his assistants in the ruins at A2. But Vess was a middle-aged half-elf and Ludinus is an old elf. He’s been around for a while, and conceivably has been fucking with this stuff for much longer.
Something else we know about Ludinus from the Explorer’s Guide to Wildemount: He survived the fall of Molaesmyr, when the corruption that spread to the Savalirwood was originally released. It was after the fall of Molaesmyr that he fled that city, went south to the Empire, and founded the Cerberus Assembly.
So what if Ludinus Da’leth was the one who caused the fall of Molaesmyr? What if he was plundering the ruins of Aeor even back then, brought some of the corrupted forest from the ruins back to Molaesmyr to experiment on it, and it blew up in his face because he was messing with something he didn’t fully understand?