Burn And Populate

[Samchung926]

Burn And Populate 72 cards, 12 sideboard 4 {Kazandu Refuge} 2 {Cavern of Souls} 5 {Forest} 5 {Mountain} 4 {Rootbound Crag} 20 lands 1 {Boartusk Liege} 2 {Furyborn Hellkite} 1 {Blightsteel Colossus} 1 {Emrakul, the Aeons Torn} 1 {Progenitus} 2 {Dragon Hatchling} 4 {Birds of Paradise} 4 {Dragonmaster Outcast} 4 {Elvish Piper} 20 creatures 4 {Nature's Lore} 2 {Naturalize} 3 {Incinerate} 2 {Rancor} 4 {Lightning Bolt} 3 {Giant Growth} 2 {Fog} 20 other spells Sideboard 2 {Fervor} 2 {Quicksilver Amulet} 2 {Naturalize} 1 {Incinerate} 1 {Rancor} 1 {Giant Growth} 1 {Fog} 1 {Overrun} 1 {Rampant Growth} 12 sideboard cards

[CajunJynx]

How does 4 bolts make this a burn deck?