Why were my Invisalign attachments, or "buttons", placed directly on my aligners and not directly on my teeth?

I picked up my first set of aligners for Invisalign Express 10 treatment yesterday and was confused to see these "buttons". My dentist had never mentioned these. Everything I have read online says these attachments should be directly on my teeth. However, mine are on the outside of the aligners. I called my dentist and the receptionist said that since my teeth are not overly crowded, he did not feel it was necessary to place them directly on my teeth at this time, but may re-evaluate later.