From what I've read it's normal for illegals to throw rocks at border patrol, so reason follows they would take the same action against our troops. There have been reports that there are many military age men in the group, some carrying firearms. 

I'm glad to see our troops can use force if credible threat presents itself instead of being overrun by force.

White House approves use of force, some law enforcement roles for border troops

https://www.militarytimes.com/news/your-military/2018/11/21/white-house-approves-use-of-force-some-law-enforcement-roles-for-border-troops/