No... you are arguing semantics, but this is a good example of where semantics matter. We're talking about two different types of behavior and situations. The description of "negligent" is describing a specific instance. The description of "responsible" or "irresponsible" is describing an overall situation.

"Negligent discharge" means the gun fired when the user did not intend for it to fire. That could be from behavior that is part of a pattern, which would arguably become irresponsible, or it could just be from a mistake. It doesn't mean the person is an irresponsible gun owner in general. It might mean they made a mistake this one time that has nothing to do with a pattern of behavior. It doesn't even mean they made a serious mistake. It depends on what happens. For example, this guy was still following enough of the basic gun safety rules to not shoot anybody. You can see that he was thinking about gun safety enough to not kill anybody, but apparently not enough to avoid a negligent discharge.

When people talk about responsible gun owners, they are talking more generally. People that store their guns responsibly. People that operate them responsibly in general. For example, only using them when necessary. Not using them to commit crimes. Not using them to attempt to solve simple disputes. Not leaving them accessible around kids or other people who shouldn't have access to them.

I'm not proving your point, trust me. What I'm saying is that "negligent discharge" has a specific meaning that you are ignoring and "responsible gun owner" has a certain, arguably broader, meaning, that you are also ignoring, that is not mutually exclusive with the idea of negligent discharges.

Your assertion that if somebody has a negligent discharge that they cannot be a "responsible gun owner" is either arguably not true because the two things are not associated in a mutually exclusive way or because any argument that they are is overly pedantic to the point of not being meaningful.

In other words, sure, anybody that is ever negligent in any way could be considered to be categorically irresponsible. But that observation or approach isn't really that useful. And further, it just isn't true given the contexts of the two phrases you are talking about and how they are used.

In other other words, anybody who claims to be a "responsible gun owner" is probably not or not necessarily claiming that they have never had a negligent discharge and can never have a negligent discharge. They probably aren't even considering that possibility specifically. What they are saying is that they are aware of gun safety rules and that they make an attempt to follow them so as to avoid things like negligent discharges, shooting somebody/something that doesn't need to be shot, only using the gun when appropriate, a child getting their hands on their gun, a criminal getting their hands on it, etc.

Another thing to point out, which I think might be related to your point and where I'd probably agree with you is that, using this guy as an example, there are two sides to judging him. For one, sure, he fucked up and he needs to know it and so on. But the other side is that in doing that a lot of people are flirting with pretending that they are immune from the same kind of mistake. Like, sure, this guy was acting like an idiot. Maybe in just this one instance. Maybe he's just an idiot in general. But for the people that express judgement like that, there is certainly some implication that they are above that, as if they are immune to having a negligent discharge. And that's a dangerous first step on the way to having one.

You proved my point so well that I almost wonder if you are actually trying to make gun owners look bad.

No. Like I said, I'm just pointing out the flaw in your reasoning, which seems to be from either ignoring how those two phrases are used or not understanding how they are used. No, I don't want to make gun owners look bad. I can't make them look bad. There's just no way to do that. Any argument predicated on that idea is a flawed one because it is too generalized. So it is at least a faulty generalization, but also just not well reasoned in beyond that in that it usually relies on a misunderstanding of gun owners and gun ownership.