Basically, this is a GNU vs BSD misunderstanding. On BSD, only wheel members can use su to become root after entering the root password. On GNU/linux anyone can su to root by entering the root password regardless of whether they belong to wheel or not.[0]

The confusion with respect to these guidelines is because some BSD-inspired GNU/linux distributions confugure their sudo to use a "wheel" group.

> once your user account is compromised the attacker is root as well

... but only if they also know the root password.

Anyway, the long and short of it is that on GNU/Linux, wheel is only relevant on distributions that use wheel in their default sudo config.

[0] https://unix.stackexchange.com/questions/4460/why-is-debian-...