So I just had the same thing happen. On my second playthrough I entered the room and Heisenberg started talking (sturm trigger) but realized I forgot some treasures and an enemy so went straight back out and down to level 1.

I went into the room where you originally get a magnum extra part and there is a soldat which breaks through the door. I killed the soldat and went back to fight sturm but he never showed up. I was taken straight to Heisenberg fight.

A theory above may be right in that I triggered sturm with Heidenberg talking and then backtracked and killed an enemy. The game may have thought the enemy was sturm and thus allowing me to skip straight to heisenberg fight.