Il existe une expression française « Avoir une chance de cocu » qui signifie avoir une chance extraordinaire.

Dans le texte cité, les voyageurs ont effectivement la chance de n’avoir pas eu à payer le taxi lors ce périple. Ils peuvent dire « Nous avons eu une chance de cocu » ou son équivalent « Nous avons eu une chance à s’en croire cocu. »

I’d translate “à s’en croire” by “to feel like” more or less literally, it is used to express something is not true (or so we hope) but we feel like it could be true anyway.

In this particular case, “cocu” refer to someone whose partner is cheating on, in France there’s an usage to say someone being lucky has to be cheated on.

“à s’en croire cocu” is idiomatic in familiar tone to express that the person saying it has had a lot of luck at an unbelievable level.

In the context of the linked article, the travelers had a lot of luck to get a nice panorama view without having to pay the usual fees in the area.