Altering depth of field is a huge part of giving a photo a unique composition. In 2012, you simply could not achieve those effects on a phone. So, this teacher

Altering depth of field is a huge part of giving a photo a unique composition. In 2012, you simply could not achieve those effects on a phone. So, this teacher was probably well aware of how hobbled her students with only phones were creatively, even if she wouldn't say it out loud for the sake of ensuring enrollment in her course.