May be not quiet sure whether they had locked the door, set the alarm, switched the washing machine off, pulled the plug out of the bath. Or any of the other countless things that we've turned back from hols to check over the years.
A few of things jump into my head here, and I'd have to do some research to take it any further
1) Birds will often be heading in the wrong direction for short periods for a variety of reasons, the same way that yachts will head somewhere other than their intended destination
2) Some Geese do weather the winter out up North.
3) Recent oddities in climate have confused many animals and plants and caused many strange behaviours
4) Huge solar storms recently have affected the local magnetic influence, and the way that birds interpret local magnetic influences in migrating is not fully understood. They may well have been kicked off course.
Number one is the most probable. even though birds migrate in one direction, they often spend a long time mulling around, especially when 3 involved
Number two is also likely, some birds do head north for reasons unknown