A shell job number isn't a process ID. jobs lists work associated with the current shell; a percent sign identifies a job when sending a signal. A plain integer identifies a PID.
Confusing these can signal an unrelated process or fail to stop the intended job. Inspect the table before acting, and leave the foreground dispatcher alone. The exercises use one idle background delay so the distinction is clear without needing a real long-running process. A command ending in & starts as background work and gives the shell a job to track. Use jobs to inspect that work, then kill %1 to target job 1. kill 1 instead addresses process 1. After signaling the job, confirm that it has ended and that the separate dispatcher process remains running.