That is correct, @tharlinsmith. The text above the image is the status (tweet) text.
To associate an image app download card with a tweet, you can do the following. First, get a list of your available image app download cards, shown in descending order.
$ twurl -H ads-api.twitter.com '/1/accounts/xxxxx/cards/image_app_download?sort_by=created_at-desc' | jq .
Then, find the specific one you want to use and get its preview_url. Next, create the tweet and include the URL.
$ twurl -X POST -H ads-api.twitter.com '/1/accounts/xxxxx/tweet/?status=Tweet text https://cards.twitter.com/cards/xxxxx/aaaa&as_user_id=0000'
The aaaa is the card ID and will appear in the URL. The as_user_id param allows you to specify the user you would like to tweet as (you have to have been granted access to tweet on behalf of this user).
Hope this helps!