It was most certainly due to the evolution of the storm. I’d call it one of the worst road surfaces you’ll see here... washboard ice. Like a mud season rumblestrip but made out of ice and melt/compression holes.
The first event probably made it wintry, but then there was prolonged light freezing rain at 23-25F in BTV that got real icy. It was icy around here with ZR at at higher 28-31F temps here. But low/mid 20s liquid gets icy on plowed stuff in a hurry.
Top it off with a decent period of 1-2”/hr that drops a quick 8-10” at the airport... I bet that’s a tough combo to battle, prolonged light icing the heavy thump.