Colorbox trigger builds clunky html instead of array
This is unfortunately just the way the colorbox module works.

Because it is possible to put any content in a views colorbox it is set up to handle anything in a very generic way, which means it doesn't handle single images in the most effective way and the trigger field way of configuring things is more complex than is needed in some cases.

I opened a similar issue about resizing the colorbox based on images, which you also cannot currently do because of the same issue of the way it has been implemented.

It is something I believe the module maintainer could fix though.
I would recommend opening a feature request issue on drupal.org at https://drupal.org/project/issues/colorbox?categories=All