And what do you think the passengers should do if they DO think they're going in the wrong direction? In detail, please.
How about going old style and actually have a conversation with a fellow passenger, mentioning the oddity in going due north for quite some time when east would be the more apparent route? But in this day and age actually talking to people is considered odd. I think anyone with a sense of direction would feel it was odd and, if brave enough to risk being corrected by the FA, raise the question to them. I sure would, but only after quite some time as a route sometimes is not very direct in the first stage of the flight. After an hour? Certainly!
I think the fact that there were only 5 pax meant that there simply wasn’t anyone with the interest or knowledge to determine that there was a problem.
If the pilots had noticed half-way, could they have turned back after ATC approval or is the flight plan non-negotiable (unless a diverstion is needed)? Could it be that they noticed after, say, one half hour and just had to keep going?