A "true" tablet will not allow you to simply touch the screen with your finger. There's essentially a sensor behind the LCD that detects the pen. Then sensors in the pen detect the pressure and what not. Others use more traditional "touch screens" which is a thin film places on top of the LCD. They do allow the use of any blunt object.
These are pretty easy to tell apart. If it's a touch screen, the stylus is typically a simple plastic stylus. No buttons or anything. If it has buttons and a removable tip, it's almost certainly a tablet.
Now this capacitive input...I'm not so familar with... I guess those HP all in one desktops have this. If you did have this method of input, you'd probably have some kind of "ad" regarding it somewhere on the computer.