I think it's more the implementation of some flowing curves unlike any production Citroen, rather than it looking like a scaled-up version of the GT.
That, and the headlights are very similar between the GT and Tubik.
Several Citroen concepts in the last few years have shared similar details.
Here's the "modern 2CV" and badly-named "Revolte":
...and here's their electric concept, the Survolt:
I've often thought the Survolt looks a bit like a Veyron in some respects, but it's probably their best concept car of recent years. They all have a similar grille going on too, and squinty headlights, so I suspect that's a design feature we're going to see appearing in production Citroens at some point.
