I hold a rank of lao shih in a Shaolin traditional style and can say that , yes, these are monks from the temple and, no, these are not sharpened spear heads, but the ratio of weight to surface area is great and painful.
The point of the exercise is to strengthen qi, specifically Wei qi which is a protective from.
Iron body training, deep meditation are ways to achieve this as well just good living, eating. Wei qi helps fight of infections as well.
My own teacher has pushed into a spear like this breaking the shaft with the front of the neck.
As a westerner, it is hard to understand the spiritual aspect of this , but to have witnessed such live demonstrations of my teacher( and the original Shaolin team from the 1970’s at the Felt Forum where I also saw a 73 year old monk break a 9inch thick, 50 lb piece of granite with is palm) the empirical evidence is undeniable.
But again, these guys have trained from around 7 years of age and dedicate their lives to training, meditation etc.
I once worked out with Shih Yang Ming, of NY, and when he punched ( showing a technique),the air cracked.
I have no doubts on the veracity of this image.