How to achive this following interactive timeline with animated background motion path.

Looking at the published content, I would think the background image is being moved with left/right motion paths, which are triggered when a timeline item is clicked.

All you need is a wide background image and a few motion paths to get it moved left or right. To achieve this interaction I guess you'd need a 4 motion paths moving left to right and 4 motion paths moving right to left. I attached a simple example with a 2 motion paths triggered on a button click to slide the background image to either direction. 

Here I found this original work as part of the ELH Challenge. You may download .story file and explore how exactly this was achieved by using the Storyline slider in combination with motion paths. Hope this will help you in your project development.