That is because the tag already has a tag wiki. The wiki got approvedwiki got approved and the excerpt got rejectedexcerpt got rejected when the first user edited it. Tag wikis are only displayed when the tag also has an excerpt. If it doesn't have an excerpt but has a wiki, nothing is displayed. If it doesn't have a wiki but has an excerpt, the excerpt is displayed with no tag wiki.
Once an excerpt is added, the wiki will be displayed correctly on the info page.
