Potential bug?

Was just playing a space marine mirror, and something weird happened. Not sure if it was a bug, or if there's a mechanic that I'm unaware of, but for a split second or two the enemy's kill team ironmaw got revealed on the map. It felt pretty scummy, because I knew that I was ahead, and so I just attacked towards where I knew his army would be since it was out of position and won of the back of it.

Was that a bug, or is there some mechanic that reveals your elites when you do something?