This suggested edit shows the wrong diff. The revision history shows what happened: first william56 suggested a retag, which was approved (revision 2), then Gilles edited the body, title and tags (revision 3). The suggested edit shows the body and title from revision 3, even though the suggested edit was against revision 1.
It is probably relevant that the suggested edit only changed tags. It may also be relevant that I initially clicked “Improve” on the suggested edit; then, when I was blocked from submitting because the retag had been approved, I went to the post and used the edit button.