  We theoretically investigate the interlayer dipolar and exchange couplings
for an array of metallic magnetic nanowires grown on top of an extended
ultrathin yttrium iron garnet film. The calculated interlayer dipolar coupling
agrees with observed anticrossings [Chen \emph{et al.}, Phys. Rev. Lett.
\textbf{120}, 217202 (2018)], concluding that the interlayer exchange coupling
is suppressed by a spacer layer between the nanowires and film. The Kittel mode
in the nanowire array couples chirally to spin waves in the film, even though
Damon-Eshbach surface modes do not exist. The chirality is suppressed when the
interlayer exchange coupling becomes strong.
