How much had you two talked about the scars before this incident? Is it something you discussed openly, or something you've avoided talking about?

While I agree with the other commenters that what he said was very cruel and hurtful, I feel like seeing something that we're not prepared for emotionally can make us react in unexpected ways that might not be the most sensitive. If I walked in on my husband bloody and cutting, my fear might make me say something that sounded very angry. I'd probably regret it later, but in the moment I would be so flooded with emotion that some mean things could come out of my mouth.

I'd compare it to catching a child in the act of doing something extremely dangerous, like running out into the street or tottering on the top of the refrigerator. You're suddenly flooded with a "oh holy shit!!!" reaction, where you grab the kid and you might yell at him or swat his bum. Maybe you say some things. You're really freaked out and your heart is pounding, but to the kid you look ANGRY. He cries. After that, you both start to calm down and you apologize, and you explain why you were upset and why you don't want him to do what he did. But in the moment where the protective instinct kicked in, you weren't yourself.