I think it depends what you're doing with it. For example, if I use my document with official letterhead to send my neighbor a fine that he should pay by mail in cash (that I can then intercept from his mailbox) - that's probably criminal. On the other hand, if I were to use my forged letterhead to write "Don't just trust anything written on a document like this, it's easy to forge!" I hope that wouldn't be.

The original incident in the article seems more like the latter to me. If I were on the jury, I certainly wouldn't convict.