I played about two months the game and I didn't found any bug (and I'm a bugs hunter ) in their scoring calculations or prizes...regarding scalability, how many times the game doesn't have bugs, it doesn't matter if are 100 are 100 million users online,all it depends on servers.
We are in 2017, all hosting providers are offering scalable solutions for servers and CDN. All you need to do when the number of visitors is increasing on your website is to pay more to your provider it's not a big deal.
For assets they are using Bitcoin blockchain, here is a problem now, but as a bitcoin fan I hope the segwit it'll be adopted soon, so we'll not see any more congestion on blockchain.
Regarding their data, sportradar and perform is providing data to most of the betting agencies and news agencies in the world, so already billions of people are accessing them daily...