Do you believe this is a computer issue or a mouse issue? Have you tested other mice to see if the problem persists? If the problem persists with a different mouse, you will know it is a problem on the computer's side.
Did you happen to save a certain preference by accident that when you perform a right-click it opens the application instead? Entirely possible, however unlikely.
Same deal with other mouse (both wireless). To the best of my knowledge I haven't done anything mouse-related. I went into mouse settings and about the only thing remotely related is setting the mouse to left hand or right hand. And even that is inconsistent. With a browser and my assorted files, the mouse buttons act correctly. Within K everything is good to go with the exception of the apps stored with Favorites. For example, I can right click anything within Settings, System, Multi-Media, Utilities, etc and I'll get the expected drop down menu. Right click on an app within Favorites and it does the same as left click. It's as though Favorites has lost its little mind.