The title! function is a convenience around the Title type, so that end-users don’t need to reference ec.title directly (though, nothing prevents users modifying the EChart chart instance).
By convention, the graph’s ‘title’ is the first object in the the ec.title vector; title! modifies this first array element, which by default is present each time an EChart is created. Further instances of Title in the ec.title vector are reserved for arbitrary text embellishments through the text! function.