Option/Alt-dragging to duplicate an object seems to be an informal convention made popular by Adobe apps. The Option key modifier is used throughout Final Cut, where you can dupe clips with Option-drag in FCP timelines. You can't do this in Premiere Pro.
An easy work around is to drag the item from the timeline into the Program Monitor Panel -- though there a number of other ways to get this done, including a simple copy & paste. The new clip then appears in the target track where the CTI is parked. You still have to select the target track but instead of mousing, you can also toggle target video tracks with Ctrl + - (adding Shift changes the audio target track).