It was just the best short term fix I could think of at the time.  Based on the code history, it looked like the user parameter was added to getWallTitle at some point and most of the callers were not changed, but I'm not sure what that original reason for that change was. I think the real problem is at a lower level, with the bad/missing titles not being handled in a better way.  

In the context that I was investigating this bug, redirecting to the user wall page as a fall back was the best thing to do out of all the other bad choices (it's better than redirecting to user "empty" for example...)  Since this is a hook, it's probably not a great solution in all scenarios.