If the system works as well as Craig says it will, then these people won't matter. If there aren't problems 3rd party reviewers will confirm that the incident was overblown. But if I was Apple I would be buying and testing Face ID with every different brand and type of sunglasses I can find, because you know some of the review sites will search high and low for a set that causes problems.
I doubt it will work with mirror sunglasses.