This is wrong.
Rooted hair means the hair is sewn into the head with a needle. 'Rooting' is the name of the process.
With most high-end customs, and figures like the Asmus Crown Gandalf, and presumable the InArt Joker, the hair is glued, not rooted. It would be impossible to root a custom head, as those heads are made of resin, and you can't puncture them with the needle used to root hair.
Hot Toys is the highest-end of rooted hair. Halloween masks at the local big box store would be the low end. To get better quality than Hot Toys, you need to move away from rooted hair, onto glued hair, which is what is happening.
Presumably, the English/Chinese translation of this process has led to InArt using the term 'rooted' incorrectly. You can tell just by looking at the head that the Joker's hair is not sewn into the head. If it was, you could see the puncture holes where the needle pierced the plastic head.