Small cluster of bees hanging under the screened bottom board in October — why, and how do I get them inside?

Hokkaido, fourth year, six hives, and winter is arriving on schedule — nights at 3°C, first snow on the mountains. Doing my final walk-round yesterday I found something odd under one hive: a fist-sized cluster of bees, maybe a few hundred, hanging on the underside of the screened floor. The varroa tray had been out for the summer, so they were clinging to the mesh from below. I have no idea how long they've been there or where they came from. Options I can think of: a tiny late cast swarm from somewhere else that chose my hive floor; bees from that colony that got outside during my last check and clustered with the queen if she'd fallen through; or just a bunch of confused bees. How do I find out, and how do I get them inside before it freezes? Brush them into the box? Smoke them up towards the entrance? If there IS a queen in that cluster, what happens when she meets the resident queen? And should the tray go in for winter anyway?