When people say you never forget how to ride a bike, they are referring to memory, also called non-declarative memory?

They are referring to "implicit" memory.

Implicit memory which is also alluded to as oblivious memory or automatic memory or as called non-declarative memory in the question utilizes past encounters to recall things without considering them. The execution of implicit memory is empowered by past encounters; regardless of to what extent back those encounters happened.