I would agree that is most likely pickling fluid/ fluid fuel mix, I noticed a partial light. The reason I say this is I have been on the headset of an aircraft inside a blast fence, it was starting to surround me and I came very close to bailing out. It could have just been fuel, it is common to see with an ignition system failure (switch systems and you get a light). Also if the aircraft had been sitting a long time the FF may be erratic so they may have elected for it to stabilize before a light. On a normal start in cold weather many PW engines put off lots of vapor.