From the fine manual page:
kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
kill -l [sigspec | exit_status]
Send the signal named by sigspec or signum to the processes named by pid or
jobspec. sigspec is etc. etc....
So what decides whether kill 1 kills the init process or jobspec 1?
with kill 1 you will send a signal to process with pid 1. To kill job 1 you have to type
the jobspec is %