No, it only uses default vanilla blocks. Right now you can't even add JSON data to the result item.
But something might be brewing because I did notice model and texture definitions in the jarfile, which might indicate upcoming custom blocks.
No i mean how did he add them. how do you even create data-packs. theres no tutorial or nothing yet.
Also for the second part.
couldn't you just edit a existing Data file for a item. (awhile back, someone edited item datas to change what they looked like.) (they would insert a sword with a certain thing on it/somthing, and it would look completely different.) Couldn't you say? edit a iron bar the same way? (make it different like how he did the op weapons,like he had RPG'S Lazer guns, nuclear launchers.) Couldn't you do the same thing, but for an iron bar it would became a different icon. giving the picture of a steel bar?
Idk im basing this off the this video.
NOW im just speculating. using that same trick for an iron bar. I HAVE NO IDEA IF ITS POSSIBLE if it is, we could edit a said furance and turn it into a power generator or somthing. which would lead to hundreds of different blocks. making mods intergrated through datapacks.
NOW THIS IS SPECULATION/WONDERING IF ITS POSSIBLE DO NOT ASSUME. i'm only asking. IS IT POSSIBLE.