I strongly doubt that the welding is the culprit. "Faulty welding" doesn't happen on something of the scale of a bridge.
You're right on. If the author of the article would have watched any of the Caltrans news conferences, they would have answered some of his theories.
The weld that he claims failed was clearly described as only being tacked, not structurally welded. That weld wasn't supposed to hold the structure together, the tie rods were, which failed. One of the improvements they are making now is to replace the tacking with a structural weld, so that even if something broke, these pieces won't come apart. The other improvements center around reducing vibration, especially in the tie rods
Who wrote that article anyway? Some guy on the internet who looks at some pictures of the repair and thinks he knows what a bunch of engineers working on the problem didn't know?