In this case, the wizard is probably smarter than the dragon. On review, it seems the wizard had 20 Int. Even if the dragon was an exceptional specimen with a rolled 18, it would be no smarter than the wizard. I don't see many DM's giving players of high Int characters packets of extra information that they can deduce from their adversaries and optimized combat tactics to make sure the advantage from their high Int comes into play. Why should dragon's get the same effective benefit? They don't have the ability "Ex: Godlike Knowledge."
Second, I don't see many ways for the dragon to improve his tactics. Surprise round = partial action. If the dragon employs what is likely his most damaging attack in this case, a blast of acid, he'll be vulnerable to counter attack. On the other hand, Darkness would protect it from targeted spells. However, this throws away the surprise round and places the dragon's first attack in a rolled initiative order. Someone will probably beat it. Casting drakness might give the group time to prepare, changing formation or casting some buff spells. And why bother casting Darkness if a breath weapon attack will either kill or severely injure the humans. At level 7, I know that 27 points of damage to 2 people coming from a dragon would leave my group in a bad position. 27 points of damage would kill or incapacitate many humans, and even veteran warriors could likely be knocked out or severely injured by it. If most cases, a breath weapon will pretty much win the battle, especially if it knocks out the cleric. let's say it does use darkness, though. With a lower caster than group, it's very vulnerable to a dispel. It can be negated with daylight. And, because it just warned the group before attacking, those events might occur before it can do anything.
On another note, I've started to dislike Greater spell focus feats. In situations where the specialty comes into play, and when spells have powerful effects balanced by a negation save, I think they tip things too much toward success, hence death. Unless there's an interest in giving casters an advantage (ie - to preserve the current situation in FR for continuity), I think they should be set aside.
Finally, if said dragon was valiantly slain by a paladin charging on his warhorse splashed toxic goo everywhere with a critical smite attack, I doubt reapersaurus would protest as much.