That's what happens when there is some sort of bug or bad reception. It happens regularly near my house till I connect to wifi. It's not exactly run away, usually the pokemon that "run away" like that are either still there, or just got caught.
It's actually the game showing you this screen cause you disconnected instead of showing what really happened. You might have caught it, it may have run, it may still be there, there's actually a chance the game didn't even register your throw. Sometimes when I re-engage a Pokemon after that it still has the berry symbol and I didn't lose a ball
