It's the digital equivalent of figuring out that a house isn't locked, and concluding that it's OK to make a copy of the furniture. FTFY
I think it's the equivalent of going down a public road and passing through a gate that was left open, onto private property.
While driving, off in the woods beside the road you notice a "no trespassing" sign, but it's not obvious that you're trespassing currently, even if you start to wonder.
A place on the disk was accessed that was unintended.
He's admitted that he kept snooping around after he fully realized that the files were online by mistake.
Besides, counterfeiting one's furniture doesn't cause any embarrassment. I'd rather equate it to photocopying your secret business plan, or your collection of naked self-pictures.