What could it mean? In fact, the concept was 18th century: John Locke said atheists need not be tolerated.
"Those are not at all to be tolerated who deny the being of a God. Promises, covenants, and oaths, which are the bonds of human society, can have no hold upon an atheist. The taking away of God, though but even in thought, dissolves all; besides also, those that by their atheism undermine and destroy all religion, can have no pretence of religion whereupon to challenge the privilege of toleration."
Ouch!
I guess there’s a better than even chance, not knowing his history, Watson was an atheist. Still he had the right to express his opinion without the sanctions these groups imposed on him. Or they should give up their government funding. They can call him a dope if they want to. A free press not constrained by progressive PC can report his accomplishments, criticize his failures, as they see them, but cancelling him disregards the boundary should be there for everyone.