As I understand it from reading their twitter replies, they were allowed to issue Winter Storm Warnings for ice rather than having to issue Ice Storm Warnings. Their Ice Storm warnings are now being used when they expect significant infrastructure (power grid) impacts, while Winter Storm Warnings are used when the ice is "only" expected to cause major travel impacts.
Here in SWMO, I figured we would have little to no issues with the power grid because air temps were pretty borderline for the entire event so most of it would not accrete on elevated surfaces. However, due to very cold ground temps, roads were super vulnerable. However, SGF does not have the ability to issue a Winter Storm Warning for Ice, so they had to decide between the advisory and an Ice Storm Warning. Based on travel impacts, I think today absolutely should have been a Winter Storm Warning, but offices are limited by the the definitions laid out.