Is it common practice to change the user information and comments to make it look like a new user's post?
This is by design.
It's a audit - specifically to test if you can recognise a good answer.
The answer is manipulated so you are not biased by recognising the name of the user or by his reputation.
I believe you will only see this happening in the First Posts queue.
Why did I fail as soon as I commented?
That part of your question is addressed here Clicking “Add comment” fails review auditClicking “Add comment” fails review audit