To qualify as a civilian one has to do more than simply look the part. How you came to find yourself in such a vulnerable state matters. After all, when everyone is wearing casual street clothing, civilian status is shared widely.
The people of Gaza overwhelmingly elected Hamas, a terrorist outfit dedicated to the destruction of Israel, as their designated representatives. Almost instantly Hamas began stockpiling weapons and using them against a more powerful foe with a solid track record of retaliation.