If Boris had announced a U turn and imposed restrictions over Christmas, I doubt the die hard "It's Christmas so I'll do what I want to" brigade would take any notice. In fact, some might have even thrown "Fuck you Boris!" parties, to spite him.
I thought he got the tone about right, and I quite liked the "little Christmas" wording. If his words make some people scale down their plans then perhaps some lives will be saved. However, some people hate Boris so much they'll tear him to pieces, even when he does something right. Haters gonna hate.