Hi Russ,
It is automatic reversing.
There are two, contra-rotating, lead-screws and alternate half-nuts are engaged when the pre-set (to bobbin width) end stops are reached. Quite a clever bit of engineering considering the overall simplicity of the design.
One thing I have learnt about hand operated winders, I would never want to challenge one of the coil winder girls at arm wrestling, especially if they have been winding with 0.5mm or so wire.

Tweakie.