Good observation :) it's the raspbian arm build -- you are chroot-ing into the exact SD card that you put into the Pi.
I don't know how exactly this sorcery works either. But I think chroot just "knows" that it needs to invoke qemu when it sees the binfmt of /bin/bash being arm.
I don't know how exactly this sorcery works either. But I think chroot just "knows" that it needs to invoke qemu when it sees the binfmt of /bin/bash being arm.