Unsent and deleted text message appeared in Messages months later
I have an iPhone 5S on iOS 9.2.1. Yesterday, I received a text from a friend I texted with a couple of months ago. The strange thing that happened was when I viewed her text on my iPhone, there was the start of a text from me I did months ago. It was text I was going to send, but changed my mind and deleted it via back spacing it.
In Settings under Messages, I have Messages set at Keep Messages 30 Days.
Why did this happen? Where are iPhone text messages stored on iOS and can I see what other texts are stored there? This really concerns me.
MacBook Pro, OS X El Capitan (10.11.2)