Code works two ways?

<?php

class Recipe{
  private $title;
  private $ingredients = array();
  private $instructions = array();
  private $yield;
  private $tags = array();
  private $source = "Alena Holligan";

  private $measurements = array(
    "tsp",
    "tbsp",
    "cup",
    "oz",
    "lb",
    "fl oz",
    "pint",
    "quart",
    "gallon",    
  );

  public function setTitle($title){
    $this->title = ucwords($title);
  }

  public function getTitle(){
    return $this->title;
  }

  public function addIngredient($item, $amount = null, $measure = null){

    if ($amount != null && !is_float($amount) && !is_int($amount)){
      exit("The amount must be a float: " . gettype($amount) . " $amount given");
    }


    if ($measure != null && !in_array(strtolower($measure), $this->measurements)){
      exit("Please enter a valid measurement: " . implode(", ", $this->measurements));
    }

    $this->ingredients[] = array(
      "item" => ucwords($item),
      "amount" => $amount,
      "measure" => strtolower($measure)
    );
  }


  public function getIngredients(){
    return $this->ingredients;
  }

  public function addTag($tag){
   $this->tags[] = strtolower($tag);
  }

  public function getTags(){
  return $this->tags;
  }

  public function addInstruction($string){
    $this->instructions[] = $string;
  }

  public function getInstructions(){
    return $this->instructions;
  }

  public function displayRecipe(){
    return $this->title . " by " . $this->source;
  }

}

<?php

include "classes/recipes.php";

$recipe1 = new Recipe();
//$recipe1->source = "Grandma Holligan";
$recipe1->setTitle("my first recipe");
$recipe1 ->addIngredient("egg", 1);
$recipe1 ->addIngredient("flour", 2, "cup");


$recipe2 = new Recipe();
//$recipe2->source = "Betty Crocker";
$recipe2->setTitle("my second recipe");

echo $recipe1->getTitle();
foreach($recipe1->getIngredients() as $ing){
  echo "\n" . $ing["amount"] . " " . $ing["measure"] . " " . $ing["item"];
};

$recipe1->addInstruction("This is my first instruction");
$recipe1->addInstruction("This is my second instruction");

echo implode("\n", $recipe1->getInstructions());


$recipe1->addTag("Breakfast");
$recipe1->addTag("Main Course");

echo implode(", ", $recipe1->getTags());
//echo $recipe1->displayRecipe();
//echo $recipe2->displayRecipe();

 private $tags = array();

 private $tag = array();

$this->tags[]