I replicated this issue on my devinstalls.
Quick fix (i suspect there is a better solutions. I was in a hurry).
Line 28, the line with:
On my test install, testing with featured image (and without) with a plain text YouTube URL.
With Featured image and Youtube Plain URL: The ”Play button” overlay should be there. However, you need to click the image and not the button. When clicking the image the play button will be hidden, and also the meta-date (as the container blocking the YouTube controls) and you can play your video.
Without Featured image and Youtube Plain URL: Should just show the video.
However (separate thread maybe), when uploading self hosted video (MP4). It just shows the URL, and in single view, the video shows up (in the content, just as in a standard post).