Hmmmm, 40° in the middle of the night in october
The AF flight to SIN departs around 11:00 or 11:30 pm from CDG, so I doubt it was "outrageously hot" inside at that time, even if the weather has been nice in Paris these last weeks (but always "cold" in mornings & evenings). They were also obviously in the middle of the night at Bucharest.
So it's another case of a lawyer who's making some noise.
But of course, it's very sad for this poor man and his family, but his health condition was likely very bad before boarding the flight.