Both is true.
They have fun, much fun - otherwise they couldn't do what they do! If you work for 60 hours in a row and still want to do a good job, a great team atmosphere is essential - no matter how much stress there was, a good laugh was always possible.
Relaxed - no, not really, that part started after the race when they went to the BN campsite to celebrate with their fans.
It's really a great atmosphere at KSM, the impression the movie gives is right.
Cheers
Werner