Yes, absolutely serious. Only the perpetrator of the crime would know exactly what was done and when. A fantasist or a time waster would not have had the knowledge to take part in that video.
If you read the press interview with Leandro (published BEFORE Madeleine's disappearance), he said that João appeared to be in a strange state that day. As you'll remember, Leandro had to accompany them to the house to give them the keys.
Do you really imagine that he went there without any form of coercion?
How does anyone not present during that "reconstruction" know whether he was given a scenario to act out?
I can't find any phsyical evidence in the files to support that what he "reconstructed" actually happened. The other guys could have come back at any moment - how on earth would he have had time to chop up a body, stuff the bits in the small fridge, change his mind, take it all out again, stuff the remains somewhere else, between them clean up all the gory mess everywhere...
IMO, it sounds more like a 10-year-old's first attempt at writing a crime story than anything plausible in those circumstances.
If one or both are indeed guilty of whatever actually happened to her (to date unknown), I don't see how it could have happened as alleged via this "reconstruction".