There’s no difference, as they both call the shutdown command.
sudo reboot = sudo shutdown -r
You would only lose data if power was lost before data was written from ZRAM (as happened with the power outage), which should not happen if you run shutdown or reboot.
Are you using Network UPS Tools? If so, the NUT monitoring client will shut down your RPi and there’s no need to run commands from openHAB.
