The animation was a bit too quick to make that behaviour obvious, so I just tried without it the first time. I thought it was a bug.

The second time I loaded an image, it did the same thing, and only then did I actually click Help.

Yeah, same thing for me. The action was too quick for me to notice that it was intentional. I would just leave the help window open on first time use until the user decides to close it. Very nicely done site though!