Border Patrol: "To see what we can catch"

So the checkpoints are supposed to be just for checking citizen status ? Here’s an agent quote from the article:
an agent on Wednesday described the Howland stop as a “random checkpoint” to “see what we can catch.”

https://bangordailynews.com/2018/06/21/news/penobscot/border-patrol-agents-question-drivers-at-i-95-checkpoint-about-citizenship/
Samm