Perhaps a more clear way to think of that is in terms of comfort and bell curves. The left extreme of the bell curve is easy to both identify and understand for anybody beyond the left end. Those are the people at the low end who perform below accepted baselines.
Less well understood are people at the right end of the bell curve, who drastically out perform other developers. In all objectivity the people at the right end of a bell curve have as much as in common with the median population swelling into the middle of the curve as the supposedly incompetent people on the left end.
Think of this in terms of risk and popularity. When you are below the middle of the bell curve everything to the right of you is better performing. You can increase your performance by moving closer to the middle of the curve by doing what is popular.
Once you get to the middle of the curve you have to make a firm decision: remain comfortable in your current posture and let popularity dictate your approach or take risks to further increase performance beyond the population median. In that regard the populations at both the extreme left and right ends of the bell curve are doing things that are extremely unpopular. You cannot become an expert without fully embracing that reality.
An expert beginner is a person at the median of the bell curve or just to the left of it. They have mastered their skills to that point and refuse to make changes or take risks necessary to advance further.
As a front-end developer I frequently encounter expert beginners. People who have mastered some framework/convention, but doesn't really understand how their technology really works and are hostile to improvements that don't make use of their favorite framework/convention. To outside observers the expert beginner is clearly identifiable as performance is objectively measured with numbers without regard for approach.