You are not the only one that has been mystified by this.
It has nothing to do with you attacking the drawn clan,the opposition sets up what is known as, 'Siege of the Stronghold'.
It costs a lot of resources to start and use.
You may or may not have seen this opperating,or may have done so, but not realised what was happening.
You may have seen the announcements in the chat,if you then go to the location, you will see birds flying round the towers.
The chief complaint about this,apart from ''we didnt attack'',but lost, is that it gives a big advantage to those clans that can use this feature, against those that cannot, or have lower achievements and skills.
They do not, I believe, to even be attacked by real players, as the game sends game troops.
Plarium generates marches that will attack them when doing their siege of the stronghold, so they need to defend against them and your clan at the same time. These marches gives points just like attacking your clan members.
Its a fun mechanic and is what makes cvc interesting, or else there will never be a fight more or less.
You need to gather your clan members and do an "Onslaught" that combine your forces for 1 big attack.
The points your opponents gained came from killing some of the troops which the game sends against their stronghold once they initiate a seige of their stronghold. They put troops into the stronghold which then battle with the various marches which the game sends.
The marches are strong and the chance for a small or medium sized clan to defeat them is small. But it is not necessary to defeat any of the marches, points are scored for each warrior killed.
To initiate a seige the stronghold must be size 4 and the clan must provide sufficient precious dust.
If both clans initiate one or more seiges and neither trouble to intervene in the enemy's efforts the winner of the category will be the one which managed to kill more of plarium's attacking troops. But it is possible to intervene. Timing can be very difficult but if a clan can attack the enemy SH while the enemy are maintaining a garrison they will score points (and concede points) depending on the outcome of the fight. The large clans aim to load up their SH only a short time before a plarium march is due to arrive and they withdraw their troops as soon as the battle with the attacking march is done (when successful). This keeps the window of opportunity for their enemy to hit their troops in the SH to a minimum.
The poster above refers to attacking by way of an onslaught because for one player to send troops against the enemy stronghold is very likely to result in a heavy defeat, therby conceding a lot of points.
Your clan would benefit from recruiting an experienced player, or one who likes to research the material about the game which has been published.