The author is obviously new to Go, and that's fine.... here's a clarification of interfaces:

Interface Pointers

Note that the author of a type that fulfills an interface and the consumer of a function that takes an interface both have full control over how much data is copied on a call to the function. You can control whether a type fulfills an interface, or whether a pointer to the type fulfills the interface. In Go, it is always easy to tell how much memory is being copied for any function call.

  type Jumper interface {
    Jump()
  }

  func MakeItJump(j Jumper) {
    // this function doesn't know what's wrapped inside the Jumper interface
    // and doesn't need to care
    j.Jump()
  }

  type Foo struct {
    data [10]int64 // array of 10 8 byte numbers = 80 bytes on a copy
  }
  func (f *Foo) Jump() {
    // we define Jump on Foo to take a copy of a pointer to a Foo.
    // this means that when we pass a *Foo into MakeItJump, 
    // just a single pointer value is copied into the interface, \
    // not the whole array inside Foo
  }

  type Bar uint8

  func (b Bar) Jump() {
    // we define Jump on Bar as taking a copy of the value of Bar
    // since we know it only needs to copy an 8 bit integer to do so
  }