I think this might not be true though. This is like saying a marathon runner can walk like an amputee using a prosthetic.
Just like anyone else with a disadvantage, people who aren't that smart develop diverse compensatory strategies to work around their intellectual limitations, and these can look very different from popular caricatures of "dumb guy". A stupid person is not as simple as a smart person might imagine.
But by talking to them you can tell. It doesn’t matter if they made a ton of money selling real estate or whatever or have lovely personality traits or… let me know if I’m missing something. You can still tell by talking to them, because the structure and detail of a smarter person’s thought process is impossible to fake*. If you are similarly smart you can mirror their structure in your head, but if you are not you will just think they are saying something weird or confusing. Whereas there is nothing stopping a smarter person from simplifying their thought process when communicating, or filtering out thoughts they don’t think will be understood by the listener. Extremely smart people can get very good at this if they are well socialized.
Just like anyone else with a disadvantage, people who aren't that smart develop diverse compensatory strategies to work around their intellectual limitations, and these can look very different from popular caricatures of "dumb guy". A stupid person is not as simple as a smart person might imagine.