I agree with berrygerry. All public talks and all service talks are heavily scripted and none go into the history of the Watchtower or any of its early leaders and personalities.
Either this Bethelite was invited (much to their regret) to speak to the congregation by the elders, or he simply went off the reservation - much to the horror of the elders.
I have heard of this happening on a few rare occasions. A former elder, CO, DO or Bethelite who has awakened, decides to use his next speaking assignment to just let go and tell his story or expose the WT. These situations, while very rare and not usually reported, do happen from time to time. As long as the speech is given in a calm manner and is not completely over the top (as was the one reported by Yondaime), the elders will lay low while the talk is going on and won't take any actions until after the meeting is over.
Perhaps at the next meeting one of the elders will mention the talk briefly and indicate that Brother So N So was having a bad night or was not feeling well, so some of what he said might not agree with current teachings and everyone should just move on and concentrate on current publications.
Elders will usually do whatever they can to discourage any further communication or discussion about the event or the subject. They will figure (correctly, it seems) that most of the audience will not really have been paying attention or will have taken special note of what the brother actually said. The few that might come to the elders to ask questions can be easily brushed off and told to just forget about what happened and what they heard. To do otherwise would show "disobedience to Jehovah and His organization."
This will very likely happen more often in the future. The Watchtower knows this. That is why they have extra elders near the stage and a brother who reads the scripted talks as they are given. Speakers who go off the script - even a little bit - will be counseled not to let that happen again, especially during a convention - unless they are one of the Governing Body members (who seem to go over the hill every so often - just because they can).
There have been there have been rare reports of speakers actually being hustled off the stage and escorted out of the Kingdom Hall when something like this happens. Occasionally, someone who has learned TTATT will just stand up while sitting in the audience and start shouting out about the Watchtower's lies and failures (a la Derek OHare in GB). The meeting is put on a brief hold while a few brothers simply remove the person from the auditorium and take them outside.
Elders and ministerial servants are informed about how to handle disturbances and out-of-control guest speakers. More often than not, they will have to face a drunk or drugged person who wandered into the Kingdom Hall rather than a speaker who decided to go off the reservation one night.
JV