Juntaro's not making his grilled cheese wrong or anything, but it might be hitting differently from the bar food because he's using butter on the pan instead of mayonnaise on the toasting surface. Doesn't have to be a lot - you'll probably end up actually using less fat by volume using mayonnaise - but it'll toast up a little more firmly and evenly, and it gives the toast a richer taste. The smoke point is also higher so you can get the cheese a little meltier before you have to take it off the pan.