Translation:If he is willing to fly, then he is crazy and he does not have to fly, but if he is not willing to fly, then he is sane and he has to fly.
I have an educated guess. There's a new bug that I've experienced myself, though not on this sentence yet. On tile exercises where the sentence is long and the tiles get pushed off the bottom of the screen, Duo fills in the tiles that have gone off the bottom of the screen. In a really long sentence it can actually fill in all the tiles. I've seen both partially filled sentences and twice I've encountered fully completed tile exercises where all I had to do was click submit. This sentence is long enough that it could well be that bug.
Of course there is nothing any contributor can do about it, so such a report is wasted. The correct procedure would be to take a screen shot and file a bug report.