Pretty obvious to me the smashing means he would devour it, as opposed to smash burgers, (American) which are also good but refer to the mode of cooking the burger patty. Putting the pineapple on the side possibly means he would eat it separately, I'd imagine. Sort of like Hamburger dessert, or maybe just give it a miss.
Speaking of which, I'll now mention a few other very popular Aussie Fish and Chip shop goodies you may not have heard of over there. Banana and Pineapple Fritters. Yep, a half banana (cut lengthways) or a ring of pineapple, which is battered and deep fried and usually served with a sprinkling of Icing Sugar. Dessert following a meal of Fish 'n' Chips which may or may not have included the Battered Sav (Savaloy) and always a few Potato Scallops. All gloriously deep fried. Fish cakes, Tassie scallops, Chiko Rolls and Spring Rolls, Dim Sims and the mysterious Vienna Steak. (Who knows what that was, but nobody cared.) Ahh!! To remember the good old days working as the potato boy in Uncle Manny's Fish Shop. No salad here folks. You could get a slice of lemon, which apart from cooked potato was the only vegetable / fruit type of thing. There may have been vegetables in the Chiko or Spring Rolls, but this was unintentional.
You must realise that all of these gastronomic treats came from our UK roots.