Correct. It was a chemical attack that Victoria did.
There was the dropship Newgrange that the Restoration forces destroyed, which was captained by Samuel Ostergaard II, son of the Commodore Samuel Ostergaard, which made the commodore go rogue when the Taurians retired their support to the Directorate. The commodore's Fortress Dropship was the Iberia, which was disabled by the virus, and crashed on Coromodir, provoking a small ice age.