That is a really interesting article. I'm not sure if you've ever been through a natural disaster. I went through the Loma Prieta earthquake in 1989. Not nearly as devastating as Japan's earthquake, but it caused some damage and lives were lost. I can remember that for months after everyone was still a little jumpy and stunned. The psychological affect and the emotional impact is something you don't expect.
Knowing how it feels from a human's perspective, it doesn't surprise me that dogs would also feel higher stress afterward. Not only would they be stressed out because of the earthquake and after shocks, but they would also be reacting to their human family members. Many families were displaced, so one could see how unsettling that would be for the dogs as well.