That makes a lot of sense with the filters, those should have both an upper and lower operational range. Tents seem to have conflicting information depending on where you look...but I'm planning on snow camping for the first time at the end of the month, using a three season tent. I have a great sleeping pad and warm enough bag, so I think it will work. Surprised you haven't tried this yet!
I consider myself pretty new even to summer camping! I was in Boy Scouts, but we car camped. It's such a different world when I have to carry everything. At least bear canisters aren't required in the winter. What the REI presenter said is winter tents make sense in high winds or places you might get a lot of snow on you as the poles are much stronger. If there were high winds forecast, I'd probably re-plan my trip to not camp. I have an REI coupon for 23% off an REI branded item. Their warmest bag is rated to 10 F as a lower limit. I'm thinking about getting that. I have a sleeping bag liner I've never used that should add more warmth, too. My summer bag is rated like 40 degrees, and I'm comfortable in that down to 40, but I think I'd be cold in anything much lower.