I don't especially love Lewis. His fiction is fine, but I find his theology badly overrated. At best it's pop theology, not scholarly, and even even as pop theology I find it shallow.

Ironically, I find his friend Tolkien's Catholic theology more thoughtfully expressed in fiction that Lewis' is in nonfiction.

Generally we restrict the notion of lying to mean willful assertions that are known to be false. But there are other problems here. We tend to divide knowledge into the categories of a posteriori (that is which justified belief through observation and experience) and a priori (that which is justified belief through structural consequence, or without experience). C.S. Lewis being a Catholic is making an assertion on an a priori facet of knowledge.

Anything is true provided you take the right postulates. You should always keep that in mind, as well as the fact that presuppositional critique on good faith belief is an uninteresting game of semantic bickering, and as a baseline itself requires epistemic certainty. Or rather, "you can't assert that because we don't know" isn't really a valid attack here. You might not know, because that lack of knowledge is entailed by your world model. C.S. Lewis knows because it is entailed by his world model.

Yes, That Hideous Strength despite being written probably 60 years ago seems dead on as a criticism of many of the things being pushed today.