It would take sackfulls of chalk to make a cloud as big as that, apart from which it is plain to see that it is streaming from the exhaust, not just appeared in one big puff from underneath the fuselage.
How much white smoke do you get in a flameout relit by the auto-igniter? Airflow into the intake must have been pretty chaotic at the start of that manoeuvre. I'd guess there would be some?