Yes, although that scenario is fictional, there is a historical basis for such a thing.
For example, here (
https://www.battlefields.org/sites/default/files/atoms/files/Gettysburg--July%203%201863--Picketts%20Charge%20Artillery%20Positions%20%28October%202019%29_0.pdf) is a map showing all the artillery placements for the third day at Gettysburg. The CSA has quite a few batteries with just two guns and even a one-gun battery. The USA has a predominance of four and six-gun batteries and only two two-gun batteries. To find out exactly how many guns each battery had at a particular time during the war you'd have to research them individually (time consuming but possible in many instances). During some quiet moments when I've read the notes for the various game titles I've seen that the original development teams seemed to have done quite a bit of research so I feel confident that even for many of the fictional battles there would be some correlation with actual numbers for the time in which it's set. However, some of the 'equal force' type scenarios appear to be completely made up just to provide an enjoyable wargame.
People may also note from the map by looking at distance scale that there are never mass concentrations of guns over a small area. Where there was suitable ground the batteries would be grouped together but they would never cram more than eight guns in 125 yards. It was simply too dangerous and after a few rounds were fired the smoke would be too thick to see through. A good reason to have a house rule limiting artillery stacking (
https://wargame.ch/board/acwgc/viewtopic.php?f=134&t=22657). On the map there are no batteries with more than six guns (larger batteries were a rarity) and if you look at the scale it can be seen that the guns are spread over a long distance. The biggest concentration seems to be the batteries of US Thompson (5), Philips (6) and Hart (4) where their combined 15 guns are spread out over 1200 feet (400 yards) so well within a limit of 8 guns per 125 yard hex. Elsewhere most batteries are further dispersed.
I usually play with artillery limits (mostly eight, sometimes six) and those limits apply at all times. [Reason: they didn't take up any less room when on the march than when limbered and, if travelling on a road, eight guns would have stretched beyond 125 yards.] Still, there must be some sacrifice to playability so we have the same limit whether they are limbered or not. According to the Union manual at the time [p24 of this manual (
https://books.google.com.au/books?id=G2cDAAAAYAAJ&printsec=frontcover&source=gbs_ge_summary_r&redir_esc=y#v=onepage&q&f=false)] a battery of six 12-pounder Napoleons had a total of 175 horses [plus there are the guns, limbers, casinos, crew and the distances themselves between them]. That's a lot to fit on a road, many of which were of dubious quality so manuals are often a 'best case' scenario.
Page 183 starts a section on distances in various situations for artillery formations. In that section, page 185 shows that when batteries are set up there must be 14 yards between each piece (8 guns X 14 = 112 yards). Once you add in the width of the piece itself (say 6 feet, or two yards [I think it's a bit more, 80 inches?]) that gives you 112 + 16 (8 guns X 2 yards) = 128 yards. So, you are pushing things to the limit to get 8 guns in a 125 yard hex (and that's according to a manual) Real-life conditions which could be a lot more difficult as the terrain would be unlikely to be completely flat and there could be anything (trees, rocks, fences, buildings etc.) 'in the way' that would prevent a 'by the manual' arrangement.