This isn't pedantic at all. The constructed number does not have to be a prime (as shown below in locofungus' example) and thus the additional step (there must be another prime, contradicting the assumption) is needed.

The cake is a lie! The cake is a lie!

I played and completed the game last November. I can clearly remember the savegame problem. After a couple of hours you had so many savegames that it took minutes to get to the save/load screen. When I realized what the problem was I started to delete the oldest savegames after every 2-3 hours of gameplay.