I've never seen that technique, using a small "anvil before.
I do note that he's just showing the easy part. He's already gotten some really high quality flint, gotten rid of all the "rind" or outer parts that are no good, broken a nodule open, created a "core" and struck off some very nice blades. All he's doing at this point is squaring them up. He's obviously very good at the earlier stages as well, because he has nice square topped flints there.