Check your settings in system preferences>trackpad>scroll & zoom.
The Rotate gesture on a trackpad can be very close to the Zoom gesture. They both use a two finger movement. Since the Zoom gesture involves spreading or pinching your fingers, if you do not maintain a perfectly horizontal/vertical movement (i.e. one of your fingers moves either up/down/left/right instead of directly toward the other finger while pinching/spreading), the Rotate gesture will be reported by the OS to Photoshop Elements. As Barbara reports, you can disable this gesture from the System Preferences.