A bug? My frigate took out 5 destroyers and 2 Lt cruisers

v. 1.25, Balance Mod.

I have a patrol frigate with 2 beam weapons and 1 minelayer lvl.2 (125kt) with 12x 10kt mines (75-95dmg x2)

I was attacked by 9 destroyers and 2 lt cruisers. Since I sacrifice speed (2 engines) for extra supply for range I don't think the frigate could outrun the attackers. I decide to attack, but discover that they carry torpedoes. I change my plan and turn for the safety of the ring. They follow behind me. Moments later, their ships begun blowing up at intervals. The frigate must have drop mines at interval. Four destroyers remain. One managed to fire a torpedo at the frigate but miss ( out of range ). Then combat ends. My frigate is safe.

I want to check on my frigate and discover that 5 mines are deployed. I check the replay. Each of the destroyers are more than 300kt, the lt cruisers more than 400kt. Each also have 170+ shield pts and 170+ armor pts. My mines have 1:1 kill but the total damage each can inflict should not be able to destroy them.