When clipping a video link from youtube, DTTG automatically populates the title field with “YouTube”. You can see the title changes from the webpage title to “YouTube” if clipped from Safari.
That’s probably a Youtube issue. I see this happening all the time, in all destination apps (like Instapaper, …).
To add another note to this, there’s currently no way to watch bookmarked Youtube videos in Picture-in-Picture on iPad, which is a really disappointing bug (?)
Another YouTube “feature”, they block this because they want to sell their Premium service for background playback. There are apps like PiP-it! and also shortcuts that try to get around this. All these solutions tend to break rather often.
There is a workaround to this I forgot to mention. When using Safari, specify website settings for Youtube to request the desktop site. This will include the name when sharing to other apps, including DTTG.
On the Mac you could try Scripts > Rename > To Web Page Title to fix the title.