Beak contact particularly between male and female birds is a way of socializing and in many cases, a prelude to mate selection. If you have ever really watched Goldfinches, I am sure you have noticed they generally travel in groups and when one flies, the remainder of the group usually follow.
Personal observations show they are very social birds. I encountered a rather large group that were feeding on some seeds heads of flowers and grasses but my attention was captured by a few off to the side of the main group.
There were three females and one male in this particular side group. The male approached the first female. She wanted no part of him.
He then moved on to the second female. A little brief beak action but nothing more.
Again he moved on to the third female. Some more beak action. I was tickled as the second female appears to have a pleased look about her.