Indeed. There were several steps missing that could (if not would) have defused the situation. The Chairs could have got an assurance from Person A that they would abide by the published diversity and anti-harassment policy of the con (which they should do with any attendee/panellist/presenter).

The Chairs could then have discussed this with the committee - with that assurance in place.

Person A could have refrained from comment, or assured people that they would abide by the con principles.

None of this happened. Result - storm.