You are right. This is a kind of advertisement which targets bitcoin users to spend bitcoin in a particular service. Something like an booklet which people in store are giving you when you have used their service.

But keep in mind that blockchain public note is not a function of bitcoin itself (by this I mean that you can not add it though bitcoin client). This is a service offered by blockchain.info and they just add this by attaching a field to their database. You can read more about it by reading their FAQ in the section public note.