How can you infer that just from its price though? :P
Maybe a significant chunk of your motivation to visit city A was to see it covered in snow and do some winter sports, so if you cancel it now you'll likely have to wait a whole year to do it again?
Or maybe you booked these trips to see some bands playing life? What if the band playing in the cheaper city is less likely to play again within your reachable area in foreseeable future?
There's a huge amount of reasons why canceling the cheaper trip may not be the best option, and I believe noticing that is what the article was actually talking about.
On the other hand, the previous price is a signal that does provide some information about the differences between travel to A and travel to B and allows to make a better-than-chance decision than treating both options as equal.
