Isn't correct! There are quantity which have three, but also quantity that have four or more ( also infinite) number of component but still remain scalar. There are quantities which have four components and are (called) spinor under Lorentz trasformations. For example the spinor field that...
The important fact to learn is that scalarity, vectoriality and, more general, tensoriality of a physical quantity isn't a property of quantity itself but it has to be defined with the respect of what transformation we are acting, e. g. Velocity is a vector with the respect of rotation ( that...