You unit races with the network being brought down, since it isn't listed as a "Before" target, FYI.
The shutdown order is the reverse of startup order, and they execute the payload on shutdown (ExecStop).
@CGamesPlay network.target's "primary purpose is for ordering things properly at shutdown: since the shutdown ordering of units in systemd is the reverse of the startup ordering, any unit that is order After=network.target can be sure that it is stopped before the network is shut down if the system is powered off."
https://www.freedesktop.org/wiki/Software/systemd/NetworkTar...