Was this non-Chaotic Good?

[AuraSeer]

IMO you're overreacting to the statement by a large margin. The way the in-character question was asked, there's no reason to assume the player's response was even intended to be meaningful. My first impression would be that he just blew the question off; even if he does feel like exposing his inner feelings to that annoying preachy cleric, who wants to get into a prolonged moral discussion while on the march through an enemy stronghold?

If a coworker came into my office right now and asked me, "Why are you drinking that soda?" I would probably respond, "Because I want to." The real reason is more complex but I don't feel like getting into a long conversation about my low blood sugar, caffeine dependency, and sleep deprivation.

Anyway, if the character's actions over time (not his words!) seem Neutral rather than Good, go ahead and tell the player he's CN. Unlike previous editions, where alignment change caused you to lose a level, in 3E it's not a big deal at all. About the only downside is that he will no longer be immune to spells like holy word and holy smite, so the cleric will have to watch where he casts them.

 

[Negative Zero]

that the player or character responded with "Because I want to kill them" really means very little, and i think that giving him a yellow card (i.e. do it again and you get penalised) was excessively harsh. in my opinion, if this really bothered you, you should have at the very least, asked the player (outside of the game) what the character's motivations for the action and comment were.

people don't often say what's really on their mind. now, i could be ascribing more roleplaying ability to your player than is appropriate, but it is possible that the character had a "good reason" like, for example an irrational fear (which might make you crazy, or at the very least ignorant, but not automatically evil).

also, i agree with the "It will probably have very little in game effect" comment. so don't sweat it too much. all that said, in the end, you're the boss, and what you say goes. just make sure everyone has fun, that is your job, afterall

~NegZ