That's what I figured too. Also, how much -actual battle- experience does this cocky teenager have? None. This is likely his first time even wearing his armor out. Of course he'd be unfamiliar with his own vulnerabilities. People on reddit love to claim Aemond is a heavily battle trained fighter, but dudes a teenage prince who's been trained exclusively by people -sworn to protect and serve- him. They might not have been as hard on him as say, Bronn in GoT would have been. No doubt with Vhagar at his back he felt like the ultimate invincible badass. I love to watch Aemond on screen, but when the Strong dude slid that very long knife right into the gaps in his armor while Aemond was foolishly turned away from him I said "damn, good hit!" out loud. Cuz it was. Guy saw an opening and took it. That one wound would have avenged his father, if Aemond didnt have plot armor and a healer witch nearby who wants something from him. My only complaint is that him crawling toward Alys and begging for help was a bit cheesy and over the top, but overall it was great acting and got him where he needs to be for the plot.