I searched 'airline life jackets' images.
Each of the many pictures suggest a similar design with the air chamber in an inverted U shape. The air chamber(s) on the chest continuing behind the neck.
Rather than a 'waistcoat' which would open and close in the front, the two chest chambers are actually sewed (or otherwise secured) together.
When I look at the FR picture above I think it suggests the jacket goes over the head, otherwise the hands would be lower down. The split you see isn't on the actual device.
It is a crappy picture though and should be fixed.