Typically this channel includes the airport arrival wait already, which is where the fifty min difference comes from, and the city to city times is to account for time taken to get to and from the city center from the airport terminal.
So is Metro to Metro starting from arrival at the airport? Why the sometimes 50 minute, sometimes 55 minute add on, rather than the general 60 minute guideline?
And City to City does my suggestion of adding transportation to the airport?
Yes, presumably because 50 minutes is about as close as an experienced passenger can cut it if you get on right as the doors close, which we are also assuming for the train, when he researched that specific flight the time presumably came out five minutes longer than you did, and yes.
