It isn't.

It's a connection you may also buy as a normal ticket. (Minimum transfer time here is 9 minutes.)

The journey planners will always give you results that adhere to minimum connecting time, so you can assume if the planner offers it, you’ll make it. This is a very comfortable connection. As @Hektor says, you only need 9 minutes at Lille.

Obviously nothing’s ever guaranteed, so part of good planning is ‘what if’. And the ‘what if’ here is that you take the 1703 to Marseille (you might need to ask at Lille for your seat reservation to be transferred under HOTNAT), or buy a new ticket on the direct Ouigo train (not covered by Eurail) at 1520.

Thanks for your replies.