The two symbols designate different destinations. The little anchor indicates that the destination is a text anchor, the page icon shows that the destination is a page.
Why the anchor sorts the way it does when you update the table of contents isn't clear. It could be entirely random. Update the toc a number of times in quick succession without changing anything in the document. It's likely that the anchor turns up in a different spot every time you update the toc. That's the kind of behaviour I've seen a few times.
Is there a way to change the text anchor into a page? I really am just trying to have the bookmark go to that page, like the rest of them.
The page icons are actually going to different sections depending on what page they are on. If a section ends up moving to page 302 for example, the bookmark will know to point to 302.
Also, that random behavior doesn't happen when I update the TOC in succession. It always moves back to the same place, right under the Table of Contents page bookmark.
I believe I figured it out. First of all, most of the bookmarks were probably generated by the TOC itself.
In terms of changing a text anchor bookmark to a page bookmark, I realized I had to get out of the text frame and just use the selection tool on the page, and then create a new bookmark.
So I've done this, and now all my icons are pages in the bookmarks bar. However, whenever I update the TOC, it still puts this bookmark immediately under TOC. I think this behavior is because this particular bookmark (called Sweeps Dates) is not actually included in the TOC (on purpose). I have it in a different style so that the TOC doesn't pick it up. But I'm guessing since the TOC generates all the other bookmarks, it sorts those when updated, and then just puts this maually created "Sweeps Dates" bookmark underneath itself, at the top of the rest of the bookmarks.
If this is a case, I don't know if there is a specific workaround to this situation. It just might be one of those minor idiosyncrasies I will have to deal with. It's not a big deal to have to move it whenever I update the TOC, and I am mainly just trying to enhance my understanding of InDesign by asking about this behavior.