Most good 8 bit and 16 bit games are designed in such a way that they naturally teach you how to play the game without explicitly telling you how to. Usually to teach you how to get past an obstacle they'll put you into a situation where it's simple to get past, but where you can't proceed until you've done it, and then later on the same obstacle will be used in more complicated settings, now that you know how it works.
Mario 1-1 has several good examples of this, and since everyone knows it, it's the best way to explain what I mean. The first teaching moment is the very first goomba. You're small, and he's right in front of you. If you don't jump you'll just die and not be able to do anything whatsoever. If you mess around with the buttons (and there's really only two that could do something here) you're going to hit jump and realize that you need to jump to get out of the way. On top of this, the first coin block is positioned so that you'll likely hit it during your jump, which teaches you that hitting blocks also is a good idea. Later on we have a great example of this sort of thing with the a set of staircase blocks with ground in the middle, immediately followed by another set of staircase blocks with a pit in the middle. If you screw up your platforming on the first set of blocks, no big deal, you're just mildly inconvenienced. But you learn that you need to be careful in such situations and therefore are ready for getting over the dangerous pit that comes next. These all teach you very basic lessons, but if you had never played a platformer before (and the audience for the game largely hadn't) you do have to learn these things.
What's interesting about Carnival Night Act 2 is that it is almost the exact opposite of this sort of approach. To get past the spinning barrel you must control it by pressing up and down. But you've never had to do that before, nor have you had to press up or down at any point in the game before (and I don't think that you have to afterwards for that matter). Now if this was the first time that you encountered a barrel you might try pressing up and down anyway by random experimentation, it's not like there's much else to do in that room. Unfortunately you have seen spinning barrels before, and they've always served as platforms. Thus you go into the room thinking "this is something that I should jump on." To make matters worse it's just almost possible to bring the barrel down far enough through jumping to get past it (and apparently it is possible with two people) which reinforces the idea in the player's mind that jumping is the way to go. Worse still, the room is thin and has a high ceiling, thus naturally encouraging you to jump.
If they really wanted you to learn to press up and down they should have made it so that the platform didn't descend when you jumped on it, but only when you pressed up or down, and/or made the room have a short enough ceiling that you could barely jump. Additionally, that should have been the first time that you saw one of those barrels. Really though they just should have taken that section out entirely, since learning the skill was frustrating even if you did figure it out (due to the up and down momentum of the barrel) and added nothing to the game past that point.