Ares was usually a lot smarter than this.
Most war deities are usually all about braun and destruction but not him.
He belonged to a special class of this bunch who was as smart as he was powerful. (Albeit never as smart as his sister.)
He understood the nuances and finer points of combat from every conceivable level, as well as possessed millions of untapped strategies for war and destruction that would send a developed nation into screaming panic overnight.
He was smart, but still.
He was goaded here because his anger had gotten the best of him, as his hatred of Abaddon had grown beyond what he was able to keep in check.
Like every other god and goddess within the heavens, he was familiar with the dragon god's face on a meticulous level.
Though this was only because it infuriated him so horrendously to see it.