Your view is extremely simplistic and just doesn't reflect the sophistication of any abstract and complex conversation.
Especially if the topic at hand is a new territory with a lot of unknown unknowns. If no-one ever explicitly says that "OK, we covered topic one and now we move on to topic two. Is there anyone who wants to add comments?", then the conversation was not very civil, was not yet over, and whoever organized the meeting was an amateur, and let the worst thing happen: Alice and Bob change topics for no reason, instead of stopping them short.
You're reading a lot into what was a fairly simple scenario with no mention of what the topics were. It came across as being an informal meeting with no agenda, moderator or stated outcomes.
About all we can assume from the scenario are the power dynamics. Alice spoke first which says it's either her meeting or she is the ranking person there - not Carol.
If it was a meeting to address the potential critical failure of a system that Carol is the most knowledgeable about, then yes, she should speak up. It could be potentially negligent to not do so, but most meetings are not that.
Especially if the topic at hand is a new territory with a lot of unknown unknowns. If no-one ever explicitly says that "OK, we covered topic one and now we move on to topic two. Is there anyone who wants to add comments?", then the conversation was not very civil, was not yet over, and whoever organized the meeting was an amateur, and let the worst thing happen: Alice and Bob change topics for no reason, instead of stopping them short.