It's hard to prove a negative, for sure. I just don't really see the data that shows the holidays had much effect. There was already a hard bend upwards well before the holidays started. It's certainly possible that the holidays made it worse and the peak ended higher than it needed to, but they certainly didn't create the winter spike.
It is evidence that other things can also lead to increased transmission.
If my hypothesis were "ONLY holidays can lead to increase transmission", then that evidence would falsify it.
But my hypothesis is that "holidays can lead to increased transmission", so that evidence doesn't falsify it.