If it was, my guess it had just ran out of juice and coasted under the aircraft. I don't remember what type of signature an SA 7 has and if it will leave much smoke. I doubt if it was unguided such as some type of RPG round. I hope the pilot was seeing things.
We just can't arm civ aircraft with PAC-3 ABM systems. Sorry to say it, but if another airliner is brought down, the border will be closed faster than you can flush a toilet.