A good quality modern chainsaw with all the correct safety guards in place is still without doubt one the most dangerous tools you can pick up. I spend around 4 hours a week with one in hand and you learn to respect the tool, and also to appreciate just how unpredictable wood is.
It's bad enough seeing all the muppets on YouTube using them without face guards, chainsaw trousers and boots, or at the very least a pair of steelies. This just takes it to a new level. Sooner or later you will bite the nose of the saw into the wood, the saw will kick back and without a brake you have a chain moving at around 80 feet per second rapidly making it's way towards your face.
Adapting an angle grinder - which has a locked on switch - not a trigger - is beyond stupid. A chain you can't stop instantly is literally a deathtrap if it kicks up into your face.