In real life, parents aren't perfect and we learn to respond better over time. This wasn't great but I wouldn't be booting him out over it or anything.
It sounds to me that your DH is quite a disempowered and underconfident parent - doesn't spend time 121 with DC, probably feels a bit bewildered and out of his depth, could do with learning more about child development and discipline through books or training course etc.
But also that your gentle parenting approach is at odds with your DH's instincts, which are to be a bit firmer. You probably need to agree a shared approach so you respond the same way. Right now he's probably being irritated by child, trying to follow what you do but feeling like it's the wrong thing and getting slowly more and more wound up.
Personally I think gentle parenting has its limits and in this situation, I'd firmly be moving child away from me eg setting down on the ground off my lap, or standing up away from them, with no risk to child but making it clear very sharply, possibly with a slightly raised voice, that scratching is unacceptable. If it upset the child a bit, so be it. Parenting that is loving but firm, confident and maintaining self control when DC are testing the boundaries.
I know a few parents who just bleat fecklessly at their DC when they do something completely out of order, like throwing stones, breaking stuff, hitting other kids etc. 'Oh don't do that, it's not nice' - well actually I think they need a much firmer approach than that. You're not their friend, you're the person who needs to make the effort to really ingrain in them that some things shouldn't be done.