In this case it’s more about shifting where the static typing occurs, since the author is still arguing for a typed business layer.

Since I/O is usually untyped, you need to cram it into a typed schema somewhere. In strictly typed languages, that must occur upon ingestion. The author is saying you can delay it by having a layer on top of the I/O transform the data in untyped fashion before being typed later on.

What's the benefit of delaying typing? By typing it at ingestion, you guarantee that invalid (with respect to structure) untrusted data will not break your code down the line. Doing otherwise means that you're manipulating untrusted data with a strong risk of forgetting that it is untrusted.

I have seen large applications (think hundreds of millions of daily users) break because of such oopses.