@Anonymous User I had a good search online and can't find any reference to the box office app being 50fps. The NowTV help page only states which channels available through their native app are broadcast in 50fps but it's only on selected devices. You could email the below address (ensuring no spaces) and ask them the question
skyboxofficesupport @ neulion.com
I have used the box office for a number of ppv events with varying results - from perfect playback to no picture or a juddery picture. On the occasions I wasn't happy with the broadcast I emailed Neulion (the third party who provide the stream) and received a full refund, albeit after some persistent complaining.