I think hashtags are more of a way to share to a group, where as mentioning with @ is a driect way of communicating that you want to give them the picture.
This is because hashtags aren't owned by anyone, but usernames are.
Hashtags are generic, certainly, but this usage was contextually relevant (with photographic proof) and clearly meant to represent that entity. Additionally, crocs is their registered trademark -- it's not unreasonable for them to search a massively popular image publishing platform for images their customers choose to share attached to their brand, nor for them to take those images and say 'Look at these happy customers!' in a non-commercial context (ie: on their website, in a photo gallery of customer photos).
I believe it's straightforwardly analogous to mailing the photo directly, though perhaps posting to every bulletin board in the country with a giant label might be a more exact match.
If anything a (public) hashtag implies you want it to be easily seen by the entity tagged -- or anyone interested in it -- as a tag doesn't specify an individual.