It's also a remarkably vacuous thing to say. Of course there's not always scientific evidence for how to respond to new threats in real time. It's perfectly reasonable to make the best decisions you can with the information available. To say what they said is to try to weaponize the totally sensible dictum to "listen to the science" in a context in which they damn well knew that it made no sense (and without any indication that they thought through how their actions might potentially erode public trust in that injunction).

We have a lot of information about a variety of respiratory viruses and masks, and almost all of it says that masks don't do much.

We're getting more information about specifically covid-19, and again that says that masks don't do much.

I’m going to be as charitable as I can be here: the experts have done a very poor job of communicating the science of mask-wearing to the general public.