And did you have to explain it to him, or was that just the first opportunity he had to raise the question, and you answered right away without him having time to figure it out himself?
I suppose it was a bit of both.
It was three of us playing. I had finished the game already by the time we started. At first, we left it to him to explore the systems on his own. He got frustrated with that and would complain that we weren't telling him what to do. So, we gradually explained more and more until we just started making decisions on our own. He was still frustrated. For example, late in to Act I, he would continue to throw his cleric in to the middle of battle as a melee fighter and die. Shortly after that, we all decided to stop playing.
There are a lot of tutorials in the early game that explain so much of this stuff that you have to explicitly dismiss that they're hard to miss.
I must have missed them, then. I don't recall any tutorials explaining anything beyond the cursory "you have to be in range to attack" or "potions heal HP" type of things. In fact, I loaded up my save and perused the tutorials again. The tutorial titled "Combat" simply tells you that there's an initiative roll, combatants are listed at the top of the screen, and during a turn, a character may take an action, bonus action, and move. It's entirely unhelpful. It may as well be a fighting game tutorial which says, "use punches and kicks to defeat your opponent."
The opening moments of the game actually require you to use your movement in turn based combat in order to continue, and you can observe which enemies can reach you or not as you approach your objective.
I got through it by just running past most everyone. Sure, you can clearly see you have to move and that you have actions to take but nothing else is explained beyond that. I think that opening sequence is a great example of the lack of explanations in the game. My buddy thought he had to kill absolutely everyone on the nautiloid. We tried twice before telling him that you can continue moving past enemies. The thought never occured to him. I can't blame him, either. All you're told is that you have to connect the transponder in a certain amount of turns and narratively, there's a sense of urgency. Nothing tells you that you don't have to kill everything on the screen. That might seem painfully obvious but that's my point: things obvious to one person are not obvious to another. That doesn't make someone stupid, either. They just have different experiences and different expectations.
Nothing in the game explains that encounters are not immutable. Nothing in the game, as far as I can remember, explains the value of environmental elements and how to leverage them in combat. Nothing explains the tactical value of oil or water on the ground. Nothing explains the concept of crowd control at all. Nothing explains how to keep backline party members safe. This is all left for the player to discover.
I've been playing Larian games for a long time and I don't remember a single one of BGIII, DOS2, or DOS ever explaining these concepts. If you walk in to these games without the understanding that you are expected to be observant and play around with the game mechanics, you will have a bad time. There are innumerable posts on the Web by people frustrated with the game because they don't know what to do. My buddy is not an isolated example. People think differently.
My buddy tried fighting in melee combat as a low-level cleric. That might be a totally valid thing to do in something like Final Fantasy. My buddy thought he had to kill every enemy on the nautiloid. Maybe that's just what you do in something like Diablo. Hell, I just finished a dungeon in Star Ocean which required exactly that. (It even told me upfront that would be the expectation of the dungeon) We are taught things which influence our decision making process. Without being told otherwise, it can be hard to understand exactly what is being asked of us as players as we try to reconcile those expections with our experiences.
My buddy didn't need to be told what to do. What he needed to be told is what he can do and why he might want to do those things. In that, Larian failed him and, in my opinion as an adoring fan of their games, they have a habit of doing so.