In a non-technical environment, it is very easy for a junior developer to end up the smartest person in the room as far as tech is concerned. Think meetings with SMEs, PMs, or Sales.
The statement is if you are "the smartest person in the room", not "the smartest person in the room in one narrow area". If SMEs, PMs and Sales people aren't smarter than you in some other areas, then you are somewhere with incompetent SMEs, PMs and Sales people.