Then it is always pronounced "o" and not "omicron" (same in the sentence with H as the feminine definite article, it should be "ee" and not "eeta"). I believe the problem is caused by linking this program to a "letter to sound" computer program instead of recording each sentence for Duolingo. You can see the same problem in the Swedish course where sometimes short words are read out as if they were abbreviations or the other way around. So, a long story short: The audio is incorrect. :-)
I completely agree. Seeing this repeatedly -- it's making me not want to bother with the course and go elsewhere. I've done ancient Greek, so I'm looking to learn the modern, but the way they're back and forth between the letter and the word is ridiculous.. No consistency. Hopefully they'll figure it out -- but this course is already out of Beta which doesn't really encourage me to think they will.
Please see my reply to another comment above. I also wrote out ομικρον and was marked wrong. If the speaker in the audio said the SOUND of the letter, I'd have typed just the letter. But when the audio provides the entire word for the letter, I type the letter's name. Yet it inconsistently jumps back and forth and marks people wrong for doing the same thing twice. This really needs to be remedied. That's not a consistent tree issue -- that's just laziness in design. Also, there is extreme confusion introducing the articles when still learning the letters without better documentation in the tips (which not everyone reads anyway).
All that to say, Duolingo's efforts are appreciated, but needs heavy work on this course (and a few others will similar problems). I truly hope they will do something, not just leave it because it's already out of Beta. I hate having to stop every lesson to keep reporting problems.