The French and other similar huge groups of people have all kinds of opinions.
If it was booed by some it means that those people for various reasons didn't like the movie. Nothing wrong with that.

Well.honestly.i was a little disappointed too. I didn't hear about this film till today and i picked it up after i read good things about it. But after i saw it.it didn't left anything behind. Somehow i had the feeling that the climax - his identity crisis as Wilson - wasn't masterated too well. Too superficial and not so well-played. But again.this is only my feeling
You don't have to be good all the time..only when it matters

France is the Philadelphia of Europethey just like booing stuff. But they do also give protracted ovations to the films that they like. They've got strong opinions
Here's what some guy on Letterboxd thinks:
Makes pretty clear why it was booed at Cannes, as all those French intellectuals who were turning away from bourgeoisie life were probably not expecting a film that basically slaps their lifestyle in their face.
https://letterboxd.com/labuzamovies/film/seconds/

This article doesn't give a clear answer to your question, but it has some interesting comments by Frankenheimer:
http://articles.latimes.com/1997-05-05/entertainment/ca-55593_1_john-frankenheimer
Personally, I would classify the film as a psychological drama rather than a thriller.
Fowler's knots? Did you say fowler's knots?

I kinda liked this movie but I don't get the THRILLER tag at all. It was more of an arthouse mellow science-fiction tale with a whole lot of exposition.
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