On the Met question, the principle here is that you can have baro error and temperature error, and if one is present but the altimeter is recording true height the other error must also be present, operating in the reverse sense.
So here we have baro on a low setting(1013) to high actual(1019) so the alt should underread. As it doesn't, the temp error is high to low, so the airmass is at lower than ISA temperatures.
Ask Alex about the flight planning!
Dick W