Those kernel modules (`ashmem` and `hwbinder`) are standard when building the Linux kernel for Android and they are already part of the upstream Linux kernel tree [1][2]. Because this solution uses containers (which share the same kernel with the host OS), these additional modules are needed.
From the ReDroid kernel modules readme:
>Custom Kernel
>If use custom kernel (5.0+), you can enable binderfs and ashmem configs; So the kernel modules in this repo are not needed any more.