Welcome to the 17th Shard! This is definitely the place for nitpicky questions - we’re brimming with the pedants of the fandom (I mean that in the best way).
I’m not the best for timeline questions, but it seems pretty likely to me that, as you suggested, he fought friends or ardents. He did participate in the war, as well - Dalinar was Dalinar, of course, but Gavilar is pretty clearly shown to be a fighter himself in those battles.