As you mentioned in IRC, this is probably just documented behavior. From reboot(8):
When called with --force or when in runlevel 0 or 6, this tool invokes
the reboot(2) system call itself (with REBOOTCOMMAND argument passed)
and directly reboots the system. Otherwise this simply invokes the
shutdown(8) tool with the appropriate arguments without passing REBOOT‐
COMMAND argument.
As you mentioned in IRC, this is probably just documented behavior. From reboot(8):
When called with --force or when in runlevel 0 or 6, this tool invokes
the reboot(2) system call itself (with REBOOTCOMMAND argument passed)
and directly reboots the system. Otherwise this simply invokes the
shutdown(8) tool with the appropriate arguments without passing REBOOT‐
COMMAND argument.