You're right. Rule 18.2(c) did change in 2010, and I quoted the old version. The updates had slipped out of my rulebook (I guess I should have pasted them in). Instead of reading "if either boat passes head to wind", it now reads "if the boat entitled to mark room passes head to wind". The change was made because some team racers had found a way to exploit that loophole to turn off rule 18. The change doesn't affect this scenerio though, because it was Artemis who tacked.

In that scenerio, rule 18 doesn't apply because boats A and B are on opposite tacks on a beat to windward (see rule 18.1(a)). It's a simple rule 10 situation.

I hope that helps,
Eric