To be clear, guy started a sync with his phone (people still do this?). In the middle of a sync he decides he wants to restart his computer, which tells him, reasonably, to wait until its done. If you were running a long-running terminal script, in the middle of a backup or large file move, or countless other tasks, any reasonable OS does exactly the same thing -- it asks the various subsystems if now is a good time, if not it delays the reboot.
He could forcefully stop the sync (which would make it not an issue, while forfeiting the work it had done thus far), and he could forcefully reboot his computer, but this has positively nothing to do with "you have to reboot your phone first".
There needs to be a moratorium on these sorts of low-info, low-effort posts. It's just pandering to a base.