It's hard to say as they are obscuring the file extensions, but even if they weren't the extensions can mean nothing (for example I could have a php site configured to use the .aspx extension). However, just jumping through their code, I can tell you they use jQuery for a least some of the client-side stuff.
If I had to guess, I would say they used ASP.NET but that's honestly just a guess. I say that because I would think it would be more likely to be some Windows-based platform otherwise they would probably be using Linux. Of course, this isn't a given. I only say that because Linux is free and it doesn't really make sense to invest in Windows licensing if you're just going to use a cross-platform technology like PHP or Java. That said, cost isn't the only thing that goes into selecting a server platform as it's entirely possible their IT staff knows Windows and doesn't know Linux while their developers only know Java.
Also, looking at the code, it does not appear to be written in a human-friendly way with the exception of what appears between the <script></script> tags. This would at least hint at some sort of "compiled" language, like ASP.NET's custom tags (i.e. <asp:label>) with some custom jQuery thrown in there by humans. However, this is just speculation (think of that adage where a bunch of philosophers are touching a different part of an elephant and each of them think it's a different animal).
So, like I said, it's difficult to tell for sure but that is my analysis. The only way to really know how it's written is to talk to the developers. I am curious as to whether people on this site have stronger analysis than I am able to provide.