Federal police shot a homeless man living on national forest land. He's now suing.

Within his rights to have the weapon on him, yes, but pointing a gun is not carrying a gun, it's brandishing, and brandishing is a no-no no matter how you slice it. Speaking as a gun owner, if you point a gun at something, that means you have intention to kill it, otherwise you shouldn't be pointing your gun at it. Too many people watch TV and Movies and think that after you point the gun to let people know that you're really, really serious, you stop and give them a chance to rethink their choices. That's not how it is; if you're drawing a gun, you have the intention to use it (at least as far as the law is concerned), so the gun should only ever come out when you've already committed to the belief that this situation requires deadly force in order to preserve the life of yourself or others and it's time to act. Otherwise, the gun stays put. That's it, there's no middle ground there, either you have to act with deadly force to save yourself and others or you don't. Anyway, brandishing in and of itself is a crime basically everywhere, IIRC. But in so many words, regardless of how they may have provoked and mishandled the situation, it's likely that any reasonable court is going to find that the officers' response to the weapon being brandished was entirely reasonable within the expectations of their job.

So, pro-tip, if you're going to introduce a gun to a situation, it had best be because you're about to use deadly force for a justifiable reason. Otherwise, just leave that shit right where it is. In point of fact, there are people who have (unknowingly) shot cops because they believed that they were acting to protect their life or someone else's, and got off with it. In all fairness, people are held accountable for it way more than they should be; cops getting shot doing no-knock raids on the wrong house (for example) is a predictable consequence, and well, play stupid games, win stupid prizes. The cops should take their licks on that and, rather than lock people up for not having the ESP to know it was the cops, maybe take a moment to wonder if they're really making smart choices here.

So was he just holding it, or pointed it at them? Those seem like two very different scenarios

It may not have been legal since he was on federal land. He wouldn't have pulled a gun on them if they had not played silly games (Most likely) I state the most likely since we don't know much about him, but there is no indication he was a hardened criminal ready to fight law enforcement. I don't like when law enforcement creates scenarios where people feel the need to defend themselves because they're confused as to what is going on.

Had they just walked up and identified themselves, I do not think anyone would have been shot.

Idaho is an open carry state, Roberts was within his rights to be holding the weapon.

Yeah, but that doesn't mean you can point it at cops.