> The real-world application (and potential danger) is when this data is combined with other data.

That's exactly the point. In this case it's only really possible to de-anonymize people who take long distance trips. But based on two data points it might be possible to know which flight or train a person travelled with.

With three different data points it might be quite unique. For example you might find out somebody travelled from Italy to Norway on Monday evening and then to France on Wednesday morning. There are probably not so many people who did a trip like that, it might come down to only one (or a handful) people who fits this itinerary. With other data sources it might be possible to uniquely identify this person.