limitation on the autopilot for single-engine coupled approaches and for an coupled back-course approach.
A LOC Backcourse approach doesn't have vertical nav. guidance but has been included in the prohibition.
It seems that in this context the A/P manual is using the term 'coupled approach' to refer to any instance of A/P using navaid input.
Most GA A/P that I've used use the term 'coupled' just to mean 'receiving & responding to input from a navigation system' and not 'receiving & responding to both vertical & horizontal navigation guidance'.