Does anyone knows what are goals for level 4 of expanion campaign? Specifically I'm asking about second objective.

At this link you can see what I'm talking about - the guy gets all the objectives but one.
https://youtu.be/MnJenh0CUkk?t=1447

In my play trough I also was unable to figure out what it was... appreciate if anyone could share the information.

I learned from game scripts the goal is to get the crystal without alerting two miners that are in the same room. However I can't figure out how to execute this :/ They always attack when the crystal crate is broken.