Why selects all page!

If you imported the PSD as a composition and did not make sure that Import as a Composition/Maintain Layer Size is checked, the small layers will have transparency and be the same size as the Comp that AE created when you imported the PSD.

I think we need a bit more on an explanation.  It looks to me like you've selected a layer which is part of a photoshop file and the edges of that layer match the comp.  If you move the layer around, you'll see that while the bounding box is the full size of the comp, the only element to move will be the 1802 element.