I encountered a couple of weird puffs of smoke at some Phish concerts.
I bet it was water vapor. If the readings are good and it doesn't happen again I wouldn't worry about it. Though sometimes white smoke is caused by coolant in the exhaust. Maybe you could remove the head and inspect it if it happens again later- especially the afternoon.
Otherwise, "white smoke" is typical in the morning regardless of temperature because the air is dense with moisture and cannot absorb it as it would after the sun is out. Therefore making the water vapor visible. I think it is blue or black smoke you are supposed to worry about.