A slip of the syntax. There is no such thing as a smoothbore rifle. Everything they had then was a smoothbore!
However, I disagree with the "aiming" part when it comes to cannons and smoothbore muskets or whatever they used.
With the roll and pitch of the ship it was difficult to hit anything at all unless the closed to less than 300 yards, and the muskets were still virtually useless at that range. I don't remember the figures, but I think 50 yards or so was a good range for the musket but even then, good armour could resist a musket ball leaving only a lead smear or a heavy dent and a bruise. But, with the packed men on the deck it was sometimes easy to hit an ordinary crewman or member of a boarding party with little or no aim at all.
Heaven help the individual who was hit though. Usually, muskets of the time (or smoothbores) were 80 calbre. The balls were as heavy as lead (pun intended). I have my Great Grandfather's cap lock, powder horn and bullet mold he used at Little Round Top. The rate of fire of those things was abysmally slow and it took a series of inventions to improve the use of rifling to the extent that it was usable. Rifles were slower firing until the hollow base balls were invented for use in a retooled musket with rifles. The expanding hollow base flared the ball and provided tooth on the rifling in the retooled musket and didn't require driving the bullet down the barrel of the rifle as was common then.
PE
My black powder smooth bore musket has a lot more accuracy than the average Brown Bess. Most of it has to do with the fact that the balls I use are sized accurately and the patch for each ball has some great modern properties. What that means is that the ball does not bounce around in the barrel and exit the muzzle going any which direction. That means my shots are a lot more accurate than those of a revolutionary era soldier. The muskets they used were manufactured to pretty loose tolerances. The bore diameter of a batch of muskets varied significantly enough to make it impossible to call each one the same caliber the way we can with modern guns today. Musket balls were formed to fit the average bore which meant that a significant number of soldiers fired ill-fitting balls. The patch you wrapped a ball in was supposed to absorb some of the slop but was not extremely effective.
The naval cannon was made in much smaller numbers to closer tolerances. This allowed for better quality control. A wealthy captain could outfit his ship with the best guns a given armoury was producing at the time. Cannon balls were iron instead of lead and therefore were harder and did not deform. Produced at lower volumes, the cannon ball diameter for a given weight didn't vary much. As long as the ball was actually round and weighted the nominal weight, it had the correct diameter.
On the ship, the best gun crews using the best cannons and hand chipped (removed rust particles and manufacturing imperfections) cannon balls and using exactly measured charges, could get surprising accuracy... given a slow rate of fire.
The situation you describe is exactly correct for typical battle conditions where the ships closed to distances of 50 yards or less. In those conditions, accuracy was completely irrelevant. Every ball is going to strike home. The battle victor is the one whose gun crews didn't panic but kept up a brisk rate of fire in the general direction of the enemy.
This was the scenario where the carronade was particularly useful. Its large bore diameter allowed it to accept a very heavy ball. These were usually special balls that were hollow and filled with musket balls. The carronade was a short ugly beast and had no real accuracy to speak of. You didn't aim those. Once the enemy was closing to boarding distance, let go with the carronade and clear the enemy deck of boarders. Every British warship had a couple of these on the quarterdeck.
In chase situations where a ship (a frigate for example) was in a stern chase with an enemy, they would use a gun called a "bow chaser". This was a forward facing 18 or 24 pounder manned by the most experienced crew. The goal was to fire into an enemy ship at pretty significant distance with hopes of bringing down rigging so that the chasing ship could catch the fleeing ship. This is the scenario where the inherent accuracy of a smooth bore cannon was used. Could a gun crew hit the target at 1 mile with every shot? Of course not. As I recall, the averages were something like 1 shot in every 10 hit the target at that distance.
Note that a "24 pounder" is not a cannon that weighs 24 pounds, but one that shoots a 24 pound ball.