Hm, it's challenging because of the new medium but maybe we could discuss a real world analogue:
You walk in to a home expecting to meet your friend, when you enter there is a man from the TV network there. You didn't expect him, his intention is just to watch you and your friend talk about television shows.
Perhaps an example that gets closer to the crux of the problem:
You're at a restaurant with a friend, and an unrelated stranger nearby can overhear the conversation. Not a participant, right? Now imagine they were sent to listen to you, and report back to the TV networks. I would say that, they have a very clear intention to participate in the conversation.
You walk in to a home expecting to meet your friend, when you enter there is a man from the TV network there. You didn't expect him, his intention is just to watch you and your friend talk about television shows.
Perhaps an example that gets closer to the crux of the problem:
You're at a restaurant with a friend, and an unrelated stranger nearby can overhear the conversation. Not a participant, right? Now imagine they were sent to listen to you, and report back to the TV networks. I would say that, they have a very clear intention to participate in the conversation.