The multi-arch (linux/amd64, linux/arm64/v8) quay.io/benz0li/ghc-musl images were created as a replacement for the utdemir/ghc-musl images (linux/amd64 only) to build the statically linked Linux amd64 and arm64 binary releases of Pandoc.
Back in 2021 there were no Linux arm64 bindists of GHC available.
Long story short: Dev Containers added to Stack repository - #6 by benz0li.
P.S: These images are also used to build the statically linked Linux amd64 and arm64 binary releases of Stack. See also