That's your hypothesis over the results, not inherent in the testing procedure. If that is the case it would show up as a specific result not be mistake for somehting else.

I'd say there being very clear trends is orders of magnitude more probable.

The way I described the experiment means the raw data would be very rich, and you should be able to see very clear things like some people being better at distinguishing than others, people being better at distinguishing between people who are otherwise similar to their culture, some people being better at pretending than others, some of the "typicals" being a lot more or less typical than others, etc. There's lots of redundancy.