Talk to him. Find out what he feels you should be doing. Ask him what he'd do if he were DM. That's a good question, in fact - what would he do in your place? Don't lead him with the question, implying there's only one logical answer, but honestly ask him how'd he'd DM the situation. You might be surprised by his answer. He might be thinking that he's playing heroic, and fully expects to be the victor.

Or, he might be looking for some cheap video-game fun. Ever play a combat vidio game where you use no tactics, just dive in and start killing things? You almost always die, but the action sure was fun? Maybe that's what he's looking for.

Another possibility is that he's wanting to play smart, but does not know what you define as smart. Find out if he's expecting to survive these little follies of his, and then ask him if he wants tips for surviving them. You know, like 'not doing that', but also maybe you can give him tips on what he could do. Sneak attacks, hit and run, archery from range to soften them up, diversions, baiting them out, whatever. And of course, having the whole party there to help him would also be good.

One common problem DM's can face with some players, is that the players assume the DM put monsters there for the players to defeat. Therefore, if you describe a bunch of tough Orc barbarians around a campfire, he's going to assume you want him to attack, and he'll happily play along. I get the impression you weren't wanting him to do that. Make sure you and he are both viewing the situation the same way.

And if he really does want to attack the Orc camps, consider humoring him, letting him do it. I wouldn't want to completely change the way I run my game, or completely rewrite my storyline, but if all I needed to do to satisfy my players is to let them slaughter an occasional camp of Orcs, I'd sacrifice a few Orcs to them.