Can you please specify your reference for that what you consider a "C1" level? Also please note that once we relax the starting conditions, allowing two years of preparations and avoiding a formal C1 exam, we can't really call it "C1 in five months."
I believe you that you sounded awesome, I believe you you've received a lot of praise for your ability, we just don't agree if that was a C1 as defined.
Otherwise, I'm sorry we've both lost this amount of time arguing past each other, when you've clearly made up your mind that no one can learn a language fluently in 5 months, to and even beyond the C1 level as described in the standards posted (the CEFR had not yet been adopted when I was in school).
PS -- And to be clear, I'm not unique, or particularly unusual in my abilities. I've known many other language learners who have learned a language fluently in under 6 months. In fact, most of my translator and interpreter colleagues probably can learn a language in about that amount of time.
PPS -- I'm offline to play with my kids. Good luck.
You never wrote clearly, have you passed any exam immediately after these five months in France? If so, how was it categorized then?