Winching 'single'.
Difficult to know without seeing the clip but bear in mind that there is a lot of cut and pasting going on with the editing.
It may have been to do with winching the casualty out of the aircraft when landing on somewhere (maybe hospital) and therefore the pilot deciding to go down to one engine so as to keep power restored rather then a full shutdown. You can shut one engine down which enables you to reduce noise and allow the blades to be stopped whilst the other engine remains at idle and continues to provide power for the winch etc - possibly.