The comment really undersells it. The fact that it is a regular number, despite not being strongly tied to something real, does make it useful. Even when you have a lot of IO wait causing an extremely large number you are being told something useful.
/*
* kernel/sched/loadavg.c
* This file contains the magic bits required to compute the global loadavg
* figure. Its a silly number but people think its important. We go through
* great pains to make it work on big machines and tickless kernels.
*/