Is that to say that you.. wait, what are you doing?

I have my router serving up TFTP with the following pxelinux.cfg (and the appropriate vmlinuz64 and initrd.img extracted from the b2d ISO):

  LABEL boot2docker
          MENU LABEL boot2docker v0.5.2
          KERNEL boot2docker/v0.5.2/vmlinuz64
          APPEND initrd=boot2docker/v0.5.2/initrd.img loglevel=3 user=docker

I guess s/he owns a second machine and boots boot2docker over the network (PXE = https://en.wikipedia.org/wiki/Preboot_Execution_Environment ) without installing anything on the second machine.

See also https://github.com/jpetazzo/pxe (especially https://github.com/jpetazzo/pxe#i-want-moar-fun).