[belter]

It's only counter intuitive, if you don't look at the whole paragraph

"We know that in a large system redundant components make random faults less likely to produce global faults. We know that in a large system redundant components make intentional faults more likely to produce global faults. In short, we know that redundancy can be protective or it can be risk creating."

Author talks about intentional faults. Like for example somebody sabotaging a specific model of CPU, or a specific airplane engine model and firmware version of that engine electronics. That would expand the fault across all redundant components.

That is not what would be defined as a really redundant system...:-)

In this case a monoculture within your redundant systems, is what causes the risk he is talking about.