From the article: 33% said they would use Bing more often after taking the Challenge
Two very different statements IMO - how many of those 33% are ever actually going to think about it again rather than just reverting to their old habits?
That raises the point that optional feedback will gain 100% of those who migrate at the time and a far lower percentage of those who will not. So that 33%, well you can half that and half again and still be short on the number who tried it.
Now if that 33% was also backed up by access log saying we had 10,000 unique vistors to this experiment and 33% of those said they were using bing now then I'd be less sceptic.
You can also bet this 33% will get turned into 33.33 recuring % or 1/3rd and from there the lie will be complete.