Pass interference illegal arm bar

[rodneyw]

Maybe someone can help me understand this, happened at my son's high school varsity game Friday. Fourth down and 26 our safety intercepts a pass
is brought down and we think it should be our ball. Ref's threw a flag on the play and this is the explanation we got. The defender used an illegal arm bar to intecept the pass. Now our safety intercepted the ball and he was 4-5 yards from the receiver and our defender, don't think he could have interferred.

Now it gets stranger the refs did not spot the ball where they say the receiver was interferred at but marked off a 15 yard penalty from the line of scrimmage and gave the ball back with a first down. Any opinions or comments that might help figure this out would be appreciated.

Thanks