This is absolutely weird. The admin panel shows a new comment awaiting moderation. When I look at it, I get confused: the origin of the trackback is a post and the receiver of the trackback is a static page.
When I look more closely, the text that causes the trackback is hardcoded text on the theme (I made a custom layout for the blog).
Now I can ignore the fact that the text is not in the blog post. But why can a static page receive a trackback?