I love how once I downloaded and installed v9.3 on my phone like the next day it wanted me to take v9.3.1 :)
That’s quality control.
the .1 was because Apple discover a small subset of older iPhones and iPads would freeze in the middle of updating to 9.3 and could not recover from the freeze. The solution was included in the iOS 9.3.1, but there was also a new potential Ransomware threat which had not yet appeared in the wild that was discovered in the meantime that Apple included in the patch to fix the freezing problem. So they recommended that everyone update, not just those who had the freeze problem.