This certainly is a warm and cuddly thread.
We have plausible explanations for what happened (finger trouble and transposition).
We have some explanations as to why it might have happened (lack of familiarity on type, rostering effects/circadian function, language and pronounciation).
What I simply cannot come to grips with is how three highly competent and qualified individuals could leave their commonsense checker back in the hotel.
In round figures the V numbers for the 400 and the 340 would be about the same for a 10 hour flight with a reasonable pax/cargo config.
When the a/c gave them 737 numbers back, they simply accepted them.
Surely this is comparable to believing a calculator when it tells you 2+2 equals 3. It is something that just doesn't happen.......