This is kind of a difficult scenario - technically, they are in fact two different pages (and you can see this when you look at the View a category button on the right, above the entry list). The first one is the overall blog, which would show every single entry. The second is viewing a specific category within that blog, which would only show entries in that specific category.
If that user posted another entry within that blog, but in a different category, the issue would resolve itself because the first link would show both entries, whereas the second would continue to show just the one.
So then you have the opposite problem, in this scenario, with the canonical link pointing to the root blog while viewing a category, instead of pointing to the category itself.