You guys seem to missing context here. The old man is walking up to the Lincoln Memorial, not antagonizing anybody. I grew up here, and forget sometimes that most people are not familiar with DC. A lot of demonstrations occur at the memorials, or end up at memorials. The Lincoln memorial has a big staircase leading up to the statue. That is why he's walking in that direction, the steps are behind those kids.
And yes, when people are walking towards the memorials, you do not block their path or stand in their face with a smirk. You also do not shout and chant and act like morons when people are doing this.
The normal thing to do is to stand out of their way and not be involved at all. The kids were being disrespectful, and acting like a big group of fools. The part people keep leaving out here is that the man said they also yelled, "Build that wall," at him.