I think this is the other shoulder. Seems like his genetic anatomy gave him shoulders that are prone to dislocating. He'll probably have the same surgery done to make it much more difficult for the shoulder to dislocate again. If he comes back like he did last time, I think he'll be strong enough to make a difference by playoff time.
THIS is why you stockpile 3Cs!
I actually have something similar although it's much more pronounced in my right shoulder than my left. Basically the shoulder joint is a ball and socket. The top of the arm is the ball, the socket is from your scapula (it's a little more complicated because of your collarbone but this isn't anatomy). For me, the bottom part of my socket is underdeveloped making it easier for the ball to "fall out" thus dislocating the shoulder. Of course, it's also easy to pop right back in, but if it affects any tendons or whatever, it can be really painful. I couldn't lift my arm above chest height without pain for about two months after I landed on my elbow playing goalie in soccer because of that.
In order to prevent it, you try to stiffen/stengthen the various tendons that hold the ball in the socket. I did this through physical therapy but if that hadn't worked, I'd have had surgery to shorten the tendon.
No idea if Berglund has something similar, but workouts would be the place it happens. There are some exercises I can't/won't do cause they're uncomfortable.