I think you will find that the tree he worked on subsequently died.
This is NOT a technique that works in general, and I would not do this on an old juniper (In fact, I would not use it at all).
There are techniques for bending big trunks that do not pose a huge risk of the tree dying, and this is not one of them. A gentle hollowing of the trunk at the spot of bending is probably the safer way. Make sure you leave a good amount of wood near the bark in areas where the bark is still alive. Best would be to do this sort of work together with someone who knows how to do this. Bending a 8cm thick trunk is not a self-evident process.