Well, now it's too late, the game has already moved on. Usually I should be able to fix a bug if someone reports it and waits before going on with the game, in this case though the bug is a bit nasty and it will take me more time to fix it.
Sun Tzu had always worked so far but here the first action completed the 'Terracotta Army' wonder, which is a special case because it affects another player, temporarily "passing the move" to him in a kind of way, and this broke the Sun Tzu effect. It would have worked if he had inverted the actions (but of course he couldn't know this).
Anyway, it's a bug and needs to be fixed, I will work on it.
Thanks for reporting it.