It turns out that is the limit for the initial installer, with further content being downloaded in the background, as happens with many mobile games these days.
Apple encourages developers to keep as much content in the cloud as possible, to be downloaded on a demand basis, such as the next level in the game, any DLC content and so on.
If this will have a practical consequence for developers, Apple could always raise the limit, but for now, without a single game tried by a consumer, don't panic too much about this limit. More on the Apple dev pages.