The query makes the assumption that you are the last editor of the post (i.e.,
LastEditorUserId is your user ID) which isn't always guaranteed to be true, because someone could have easily made an edit after you did. This is why the
PostHistory table exists, since it contains the full revision history for any given post.
Additionally, as Jeremy Banks points out, the data used by the Data Explorer isn't always up-to-date, so even in the case of valid queries the Data Explorer results can occasionally lag behind those of the actual sites. To check when the data was last updated, you can take a look at the Data Explorer main page and find the date above for "most recent" in each site listing (image courtesy Michael Mrozek):
This value is also shown in the sidebar of the queries page. In this particular case, the data is relatively fresh, so the variance caused by that shouldn't be too significant.