Why doesn't a systemd-nspawn server restart after reboot or crash?

I have an otherwise working systemd-nspawn managed container (minimal Ubuntu 16.04 from debootstrap) but I cannot make it restart when crashed/rebooted.

The unit file is

# cat /etc/systemd/nspawn/minec.nspawn

[Exec]
Boot=yes

[Network]
Bridge=minec

[Service]
ExecStartPre=-/sbin/ip link del vb-minec
Restart=always

Specifically, I was expecting Restart=always to respawn the system if it is powered off or rebooted (from within the container) or otherwise crash.

I was wondering if the reason is not because systemd sees a shutdown/ poweroff as the equivalent of a systemctl stop? If this is the case - is there a way to change this behaviour?

Otherwise, is there anything else to setup to have it restart?