Did rask have a penchant for it at the time? Does Wallstedt? Honestly asking, I don't know.
If a goalie is quick to emotion and breaks his stick, it means nothing. If a goalie is slow to emotion and breaks his stick, it means much.
Tuukka was absolutely an emotional goalie, especially his younger self. Jesper doesn't give me that impression, but he is very competitive. You kinda need to reach the heights he already has. Not overly surprising he's not handling losing very well, especially with how close he is to the big leagues. There's a double whammy of losing those NHL opportunities and getting pumped five-goose for the 20th loss of the campaign down in the minors, figuratively speaking.
I wouldn't be worried about it. Frustration is part of competition. Hell, I'd me more worried if it didn't affect him at all.