I would say they made a decision by default...

in the train example, if they do nothing, (that is they don't get on the train) the default is staying in town...

and if they were on the train, and thinking about getting off a stop before their normal station to go shopping, or to visist a friend, and let the train stop, and didn't get off, again the decision is one of default... they did nothing to change the status....

lots of decisions are made by default... people are often dissatisfied with their job, or their spouse, or their homes or apartments... but changing requires them to do something, to make some sort of effort... they decide not to make any special effort and nothing changes...

sometimes they get divorced by default... if one spouse wants a change,and starts divorce proceeding, and the other doesn't take any action, they are likely to find themselved divorced--by default.