If remember correctly this specific calc, this is from a not very good YT video with a lot of errors that we laugh at sometimes in the theorycrafting community 
You can see that’s it’s bad because the calc is unfinished without components / augments, only using legendaries etc. Made by someone who focused on clicks rather than quality and is quite new to Grim Dawn. RektByProtoss made a video about it.
Here you have a better build guide for this character
If you want to level a character with this build in mind, you should level as a Chaos character imo not Fire like in this guide. We have some Chaos leveling beginner builds in the Beginner Compendium but not like that specifically - some casters / melee with Sigil for example.
If you want the same style (guns + doom bolt), you could dual wield these Bloodsworn Repeater - Items - Grim Dawn Item Database but I don’t know a beginner guide for them specifically. Maybe there’s sth on Youtube.