That will make a 2-by-2 array of plots and display the image in slot #1 (the upper left slot). That's where you told it do display. If you don't want that, then make a different third argument to subplot() or maybe just don't use subplot at all. In general:
imshow(rgbImage, 'Parent', handleToAxesThatYouWant);
or
axes(handleToAxesThatYouWant);
imshow(rgbImage);
