For that example of the street, technically the office...the location is simply a question of saying, “We would like to meet, and we can meet here at this moment. Let's chat.” That is an arranged meeting.
Our point is that you are choosing to arrange this meeting. You could still, if someone bumps into you, say, “Actually I don't want to talk to you,” and then move away. You should have the authority to say, “I don't want to engage and meet with you as a lobbyist.”
Whether it's in the office, on the street, at the airport or wherever, as long as you said, “Yep, let's meet. Let's chat,” you've acknowledged that this is an arranged meeting that you are going to have. You could have it at that moment, or you can have it three days later or at some other time.