Is it still kill stealing if.....

[choctaw111]

That's a thin line there.
The enemy plane was set on fire by another player which typically is a no-no to shoot down yourself. Then again the enemy plane is still shooting at your team mate.
That's a tough call really.
You don't know what happened to the pilot who set the enemy ablaze?
If he broke off after he set the enemy plane on fire and the enemy is still shooting at a team mate, then I would say you were right in what you did.
If the team mate who set the enemy plane on fire was still pursuing him after it was set of fire, then you dove in and finished it off, then there may be some accusations flying around.