The guards at the tomb of the unknown soldier are well known for this. There's videos of them yelling at people all over YouTube anyone wanted to see.
Their entire job is to maintain the peaceful and respectful atmosphere in the cemetery, no matter who it may be disrupting that.
The real story here is that the Secretary of the god-gamned Military and his entourage don't know that and had to be reminded to mind their manners at arguably the most important US military memorial in the world. That the headline is putting the focus not on the transgression, but on the soldier who called it out is disingenuous.