Yes I can confirm it’s BabylonJS ahah 
Eiffage - Hyperion project @ Bordeaux (France) ; by Axeon Software (This was our first PBR testing on BJS).
About our UI used here, we often need an html design because 3D realtime app is just another media among others (images, videos, etc), and so data are handled above the 3D app. We have clickable objects inside the 3D app, not using BJS GUI 3D here but pick detection (it’s only recently we’ve give a try on GUI 3D, which is fine by the way).
So about doing this UI with BJS GUI, I can’t say yes or no 'cause I haven’t played too much with it actually. But I guess basic things could surely be made using BJS GUI. Maybe things like drop-down menus are a bit harder, or even not possible? (but I can’t say :D). Also if you’re a lot comfortable with css you will probably prefer using it. You have the choice 