In the 0:44th second of the Android Nougat Statue Unwrapping video, which you can watch below, you can see the image of the new statue along with its name. (as seen in the above screenshot).
Android 4.0 to 4.4.4 spanned three major versions (Ice Cream Sandwich, Jelly Bean, KitKat), Android 2.0 to 2.3 had (Eclair, Froyo and Gingerbread), while Android 1.5 and 1.6, were Cupcake and Donut respectively.
Google only started the major number upgrades for Android versions since the release of Android 5.0 Lollipop. So, it is not remotely surprising that Android Nougat is Android 7.0.