The reason for the explosion is due to the fact that when baking soda and vinegar mix a chemical reaction occurs and henceforth it fizzes. (although it explodes in the comic that's just dramatization)
Hi! Welcome to Burny's What would like?
Just a burger please
Well at least we live up to our name
The chemical change in this comic is due to the fact the the grill in the back converted the propane into fire causing the grill to ignite and start cooking the burger to the point of being able to classify it as "burnt"