Most likely you had an error made by and overuse of your RAM or by a combination of miscommunication between your phone and the Niantic Servers due your connection.
Happens from time to time, don't worry about your prize, most likely you won it anyway, but the game won't tell you what you won so you will have to check your storage thorougly.
Was on this screen for 5 minutes
I was doing a distance battle with a friend, and the image below is what my screen had for about 5 minutes, I know it wasnt just frozen because both tyranitar were doing that idle animation and the thing under the opposing tyranitar was moving.
My friend said that the battle was completed for him and he got a sinnoh stone out of it, while in my journal theres no record of the battle
Any idea what happened?

Answers
> most likely you won it anyway
No, he should have lost since the opponent was able to keep fighting and his pokemon were just sitting there doing nothing. At least that is what happened the two times I've experienced this.
Still don't need to worry about losing prizes or anything. Your 3 trainer rewards and 1 leader reward per day are not lost if you error out or have a full item bag. If anything ever goes wrong and you don't get the reward for the battle, just fix the problem then do another battle and you will get the reward for that.