My guess is your bees weren't flying because it was too windy, not too cold. Lots of bees still fly when temps dip below the fifties, some even fly in the forties and some on here have reported bees even flying in the upper thirties, like Brian Bray.
Opening a hive for a quick look may not be a big deal, but it might be, all depends on the highs and lows in that time period.
If you're in a warm up trend, you may be able to get away with a quick look, once they've clustered, but remember, when you open that hive, you have heat escape, which could be very detrimental to a hive, so be careful in winter and give just a quick look, if needed.
Most in the dead of winter keep their hives closed and may weigh them or lift them to get a feel for food adequacy, but in cold temps you are putting a hive in cluster at extreme risk by allowing heat to escape even for a look in cold temps. If you have to, do so at the hottest point of the day.
Others will chime in, who actually live and keep bees in very cold temps, beekeepers who actually have "winters" and can give you specifics. I'm in the deep south, our winters may consist of a few days here or there where temps go below freezing, and even then, on those same days, it may warm into the 70's.
...JP