he was trying to take a picture, popped his head out the train door and a heavy object hit his head."
I didn't know they had manually opening doors/windows on the Paris metro?
I think you're confusing a quote from someone who wasn't there and is not even an objective non-observer, as processed through a journalist or two, for a technically exact statement of fact.
The picture in this
report from le Parisien shows one of the trains:
LP/Olivier Boitet
A slim teenager could probably get out of one of those windows, or at least get his head and more out of it. Which of those he was trying to do (or possibly something else) may be a difference without a distinction, since he didn't succeed in doing any of them.
That French report says he was found between two carriages of the train, which is suggestive, but that too is given as hearsay at that stage.