There is a a follow up post that is linked in the link you posted which says the following: As it turns out, Dropbox views/opens certain file types in order to

There is a a follow up post that is linked in the link you posted which says the following: As it turns out, Dropbox views/opens certain file types in order to convert them to a compatible format so they are easily accessible via web browser for its users.  This makes sense and is common practice for many cloud storage services to provide the convenience of browser access while not needing any additional software to open these documents.