From what I can tell they use ASPX on their backend for the most part. So assuming that typescript is mostly used for frontend wasn't that far of a stretch.
I've seen some great UIs that are cobbled together from bootstrap + several extensions with a bunch of monkey-patched CSS and other jQuery extensions... the code is a hodge-podge mess that I didn't enjoy working with, but the UI itself was quite pretty/useful.
I've seen the opposite as well. One does not beget the other. On my current project, I'm often doing a followup pass on the UI/UX for this project.
Sure it does. We often have designers jumping in and programming UI code themselves. Teaching them all about type systems would be very time consuming.