Build FreeBSD Docker image using Ubuntu host OS
As you can't build a docker image for an arm kernel from a x86 one neither.

Nor can't you build an image with a glibc lib targetting a 4.x kernel on a host running a 3.X kernel.

Docker isolate processes and give a virtual filesystem but that's still the host kernel who own the process, so obviously without a layer of hardware virtualization like virtualbox, vmware, xen, kvm, there's no chance to build an image with binaries made for a different kernel type.