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The thumbnail of that video is veeeery misleading. You cán craft items using custom crafting recipes in datapacks, but you cannot add new items to the game. so... You don't need a resource pack in order to make new crafting recipes. You do need a datapack to store your recipes in, which is basically a bunch of folders, structured in a particular way, as explained here: https://minecraft.gamepedia.com/Data_pack
You do not want to use a resource pack for custom items, because resource packs can only alter existing textures and/or sounds. If you want to add new items to the game, you'll have to use mods or make a mod yourself.
Not quite sure how Logdotzip did it but it is done with a resource pack, since 1.8 you have been able to change the textures of items based on their durability. If you combine this with not showing the durability of the items, you can create “custom” items.
With Optifine installed it is possible to change the textures of almost all items based on their name (and mobs based on the biome.)
I hope this answered your question, I believe Logdotzip released the data pack for his first video on custom crafting and an example for the Optifine would be Itembound.