You can't hear the "o" in the listening exercise.
I'm not Czech, so I might have it wrong, but as far as I know, prepositions alone are not stressed in Czech language and because of that they kind of merge with the following word.
Even if that would be the case, you still cannot hear that this letter is merged with the following word.
It is indeed incorrect. I have disabled the audio exercise.
Why is 'two months ago mátej proposed to her' wrong?