It's not unusual for it to snow in Tasmania in summer time. It even snows here on the mainland from time to time in summer.
As for an explanation, BoM is probably your best bet. Probably something to do with lows and the direction of the wind. The Tasmanian forecast does mention a trough crossing and moving away to the east, and southerly winds. I expect that's what has brought the precipitation and meant it's cold enough to fall as snow.
