No. The Peter Principle states that in a hierarchical organization, everyone gets promoted until they reach their level of incompetence. This means we could conclude that if someone has stopped being promoted, they are incompetent in their current position.
However, if we assume that promotions are generally given to the most competent individuals within a group, then ultimately, while such a person may be incompetent, they will still be the least incompetent option compared to others.