The way it reads, they didn't know how POSIX permissions work, and maybe still don't. The article says that sudo needs to be owned by uid 0, but does not mention the critical suid bit. Maybe they just recursively copied /usr without preserving permissions?
Also, the mention of sudo makes it pretty clear that they did not do this in an interactive root shell (obtainable with sudo -s/-i or su if there is a root pw). If you do this kind of shenanigans, you better have multiple open root shells in front of you, and some statically linked binaries (busybox?) to recover from the inevitable chaos of missing binaries, shared libraries, and dynamic loaders that you'll transiently have.[1] It's not impossible to perform, but requires careful planning and a good understanding.
[1] Though if /usr was indeed copied without preserving permissions, recovering would have been very tedious.