Could EntityState.Modified cause Insert operation to be performed

I am reading the following tutorial about entity framework 6 Link. And inside the section named ”Adding an Edit Page for Instructors”, the author wrote the following code inside the Post edit action method:-

[HttpPost, ActionName("Edit")]
[ValidateAntiForgeryToken]
public ActionResult EditPost(int? id)
{
    if (id == null)
    {
        return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
    }
    var instructorToUpdate = db.Instructors
       .Include(i => i.OfficeAssignment)
       .Where(i => i.ID == id)
       .Single();

    if (TryUpdateModel(instructorToUpdate, "",
       new string[] { "LastName", "FirstMidName", "HireDate", "OfficeAssignment" }))
    {
       try
       {
          if (String.IsNullOrWhiteSpace(instructorToUpdate.OfficeAssignment.Location))
          {
             instructorToUpdate.OfficeAssignment = null;
          }

          db.Entry(instructorToUpdate).State = EntityState.Modified;
          db.SaveChanges();

          return RedirectToAction("Index");
       }
       catch (RetryLimitExceededException /* dex */)
      {
         //Log the error (uncomment dex variable name and add a line here to write a log.
         ModelState.AddModelError("", "Unable to save changes. Try again, and if the problem persists, see your system administrator.");
      }
   }
   return View(instructorToUpdate);
}

This code will cover these three conditions:-

• If the user clears the office assignment and it originally had a value, you must remove and delete the OfficeAssignment entity.
• If the user enters an office assignment value and it originally was empty, you must create a new OfficeAssignment entity.
• If the user changes the value of an office assignment, you must change the value in an existing OfficeAssignment entity.

So does this means that

db.Entry(instructorToUpdate).State = EntityState.Modified;

will cause an insert statement to be performed for the OfficeAssignment record incase the Instructor did not have a prevouse OfficeAssignment object ? and what is the rule that govern this ?

here is the complete model diagram:-