When CS5 was designed, touchscreens were not common and relevant so the software wasn't designed for that.
If you want pinch to zoom, you have to get Adobe Creative Cloud which is the latest version of the software. CS5 is pretty ancient at this point. The Photoshop equivalent to still running Windows XP.
For example Lightroom does have pinch to zoom and it works beautifully.
The Surface Dial works beautifully in CS5 for zooming in and out. Just twist one way to zoom in and the other to zoom out.