If a parent yelled at me for taking a picture of their kid jumping over a bench repeatedly, I would say that parent has a distorted view of what is acceptable behavior in adults, hers as much as mine.
And perhaps also what is acceptable behavior in children. More even than children who are unruly, children who are allowed to give others the finger.
What does it mean to "interact"? Is watching a child jumping over a bench considered interacting? Are we to keep our eyes averted now, for fear of causing alarm? If a ball rolls to us, are we not to pick it up and toss it back or hand it to the child? If we are walking along, and children pass by, are we not to say hello or even nod?
Are we to constantly fear the wrath and judgment of others if we so much as glance at kids without their protectors' permission? There must be a limit somewhere. A person following children around with a camera is not comparable to someone sitting on a bench taking pictures of a child romping, as the OP was doing.