You don't get gusts with calm, you gets gusts with wind. The night Madeleieine disappeared was windy with gusts so an open window would create a differential in air pressure which should have been immediately noticeable on opening any exterior door.
You can get sudden gusts John, with relative calm in between.
And you can get the calm before the storm too. (at the time of Matts visit).
So long as the differentuial in air pressure is insuffient to overcome the friction of the hinges and insufficient tio create a force able to move the door any minor draught would unlikely be noticeable to anyone walking in from outside.
As kate pulled the door to, a greater surface of door presented itself to the gust and whoosh the door closed. At the same time as the door was being closed, the gap was decreasing and the draft was trying to get thru a smaller gap.
The speed of that draft was forced to rise in a similar way, which when a busy motorway has two lanes closed, traffick moves slowly before the road narrowing, but speeds up as it goes through the narrow part.
I am not very good at explaining things, hope that the reader can understand.
Please see my post @12.23.35 am today on thread "We must reconstruct Maddie’s fateful night" says former Portuguese police chief.