config is /sbin/e-smith/config
The config command comes from the nethserve-lib package, it’s a core package, you can’t have NethServer without it.
Maybe you “adjusted” the PATH variable.
Default is /sbin/e-smith:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/opt/puppetlabs/bin:/root/bin