No rhyme nor reason to what dahlias sometimes do. I've dug up dahlias in winter only to find a shoot growing when it shouldn't be budding for another 6 months. I had a tuber laying on the ground since February without being planted near my chair and in Sept it started sending up a shoot. It is now about 12-16 inches high but WAAY past the time it would be able to bloom so eventually I'll have to cut off the shoot and replant it next year.

Can't explain why you got MANY shoots except you may be correct that the weather is so nice, it is sending up multiple shoots this late. There is no harm in simply cutting off the shoots and letting it winter as normal. If you let the shoots grow, they will simply grow until they run out of steam and will then simply fall over. And hopefully send up the same number of shoots as now, only next May or June when it is supposed to.