I agree with you that the budgie is not suited for the harness, and the info provided from your store is much clearer.
I only got confused from
http://theparrotuniversity.com/content/aviator-bird-harness, this is also the source of the photo's I posted and are definitely not user submitted. They have been sent to parrotuniversity.com by a user, but have been placed there intentionally by the owner of that website (looking at the sourcecode of that website, the photo's are not random generated from a db where random people may place photo's of their bird).
And, there they advise the harness for small sized parakeets, a set where the budgie fits in my opinion.
This is what frustrates me: You are right that
the harness is not suited for a budgie, and that should be made very VERY clear for all budgie owners!
But, I am very disappointed in the quality of advertisement from the parrotuniversity.com themselves. Their way of advertising let people think that their budgie fits in the harness which is wrong!