From QMetaObject Detailed Description:
method() and methodCount() provide information about a class's meta-methods (signals, slots and other invokable member functions).
and "invokable" links to Q_INVOKABLE in the QObject docs. QMetaMethod specifically documents:
A method will only be registered with the meta-object system if it is a slot, a signal, or declared with the Q_INVOKABLE macro. Constructors can also be registered with Q_INVOKABLE.