Not sure reason for the “historic” term, but may be due to the lowest barometric pressure recorded for the date? Big deal made of this on local CO media...
Talking heads kept hyping the “bomb cyclone”...From the term bombogenesis...
elteemike is correct. Historic is in reference to the pace of the pressure drop and low recording of the barometric pressure. A couple of places recorded their lowest pressure on record in this storm.
Otherwise, the wind and snow were not historic.
The stupid people that insisted on getting out in the blizzard on the other hand... stay home, seriously.