The line shown in that page do install the kernel modules, but not the kernel itself. It should be 'make && make install modules_install'. Reproducible: Always Steps to Reproduce: 1.Visit the link i provided. 2. 3.
i'm pretty sure default kernel install copies kernel to / while the 'Gentoo way' is to use /boot that said, if you look down to the section right after it, we tell you how to install the kernel