I don't consider it a major error in this context. An error maybe, and proves you read the article. But in this context of TB's, I suspect they almost never deform, they are radial limited by design application. And the paper clip is IMO a useful analogy to help one causally visualize the reverse stress issue, since few will bend a paper clip a million+ times to witness the stress reversal fatigue issue, but bending 25? times everybody should get the "clip" point.