It might be but I tend to believe the number of recent burglaries in his neighborhood probably had the most effect on his state of mind. He was looking out for his other neighbors by keeping an eye on Trayvon until the cops could show up. Unfortunately Trayvon decided to come back after running away from Mr. Zimmerman and attacked him. If that had not happened Trayvon would have never been shot.
How do you account for the girlfriend's testimony?
Of course, she could be making it up, except for the call timing, which would be not from her, but from the cell carrier.