What's happened is that the text you deleted included the object anchor for the graphic. The object anchor is a logical connector that links a floating graphic (or other floating object) to the text of the document.
Undo the deletion at once by pressing Ctrl+Z or choosing Edit » Undo. Then turn on the display of object anchors so that you can see where objects are anchored: choose Tools » Options, click the View tab, check the "Object anchors" box, and click the OK button. Select the graphic and check where the anchor is (see Figure 4-14) before deleting adjacent text.
Figure 4-14. Object anchors add to the clutter in a document window, but they can help you avoid accidentally deleting graphics and other objects.