A little common sense. A large tactical unit is essentially marching in your direction.
Do you think that they want you to:
a) stand in front of them without moving to have a nice long chat about the daily events with them
b) move out of the way - clear the area
c) approach them head-on which can easily be misinterpreted as a provocation, threat, or refusal to disperse
If you chose A or B, you might get a small push, like the old man did, because you're inept.
If the old man was trying to hand something to them, he could have left it on the ground far in advance of them and they would pick it up as they advanced.
This won't make any sense to those that see the police as evil incarnate, but they are the loud minority anyway. They get far too much air time because media outlets like CNN make money off drama. There are bad people, including bad cops, out there. But don't lose the plot.