This is because you are still in the DVD menu, you need to select your slideshow to play it full.
When you insert your created DVD into a stand-alone DVD player connected to a TV, it does not start playing the slideshow straight away. Instead in goes into a menu screen. This is what you are seeing. It simply shows a preview of your slideshow in a small window on the screen (thumbnail sized). To start the slideshow playing, i.e. full screen with all the photos shown, select the slideshow using your DVD remote control. I.e. with the remote control arrow and enter buttons. It is just the same as with a normal DVD movie you would buy in a shop where it brings up an initial menu and you have to select enter on 'Play film' to actually start it playing the film.