If you are invited to a meeting as a guest speaker, understand it is not to make the people know all what you know. God simply wants to pass a message through you to that audience. Find out what it is and focus on that.
It is unethical to start addressing a difference you have with another guest speaker at the meeting. I have witnessed situations where someone walks into the auditorium and the speaker changes his focus and sees this as an opportunity to address this other person. This is simply juvenile.
Focus on the people you were invited to speak to. To attempt to use the pulpit and not a one on one conversation to sort things out is a display of cowardice.
Also if you are the host and you invited a guest speaker there is no need to get up after he or she has spoken and begin to pass comments which are subliminal messages to your congregation that you also knew all he has said. Don’t belittle your guest in front of your congregation. If you think you knew it all, why invite him?
This may show your motive was not for the guest speaker to be a blessing to your people but you using the invitation as leverage for something else.