Types “怎么可能？”；“静态类型”；及；“动态类型”；会有所不同吗？

根据Nim手册，变量类型为“静态类型”，而变量在内存中指向的实际值为“动态类型”

它们怎么可能是不同类型的呢？我认为给变量分配错误的类型是错误的

import typetraits

type
  Person = ref object of RootObj
    name*: string
    age: int

  Student = ref object of Person # a student is a person
    id: int

method sayHi(p: Person) {.base.} =
  echo "I'm a person"

method sayHi(s: Student) =
  echo "I'm a student"

var student = Student(name: "Peter", age: 30, id: 10)
var person: Person = student # valid assignment to base type
echo person.repr # contains id as well
echo name(person.type) # static type = Person
person.sayHi() # dynamic type = I'm a student