Well technically you can't, in the sense that chroot has no idea you're doing it... the magic of binfmt support in the kernel (setup for qemu by the post-install script for qemu-user-static I believe) basically lets you run any architecture's binary that qemu-user-* supports just by trying to execute it natively, it basically just translates the execution of "./other-arch-cmd" into "qemu-user-static ./other-arch-cmd".

Thank you. That makes sense. Even though there is a translation layer via qemu-user-static, still having the facilities to have that transparently is very fantastic. And also very fascinating and a revelation to learn about for a bearded old timer like me who has never seen it before.