Like most ceratopsians, it is assumed that Arrhinoceratops lived in moderate sized herds or small family units at the very least, like modern elephants. The reason that an animal like Arrhinoceratops would not want to live in a very large herd has more to do with the sheer size of the animal. Arrhinoceratops was approximately 6 meters (19.7 feet) long and filled most of that length with muscle and belly. How do we know it was so long considering that we have found only a skull to describe this dinosaur off of? The powers of educated guesses and estimates based on other ceratopsian skeletons and understood ratios between skull size and body size have given us a fairly accurate way to hypothesize estimates like this. All said and done, Arrhinoceratops was probably too large for a large sized herd. A family unit of two mothers and a father, or as elephants are wont to herd as three to four mothers and their children typically, could easily care for three to four young and keep them safe from predators with their size and weapons.
Speaking of those babies there, the number being so small in a herd makes sense. It makes a lot of sense actually. Large mammals have small numbers of young because they care for them and raise them as well as possible in the dangerous wild. Assuming that all dinosaurs always laid eggs, some of those eggs would not have hatched or may have been eaten and the tiny, by mom's standards, pups may have faced predatory dangers and the clumsiness of adults from the moment they emerged, further reducing the chances of survival to herd-on-the-move living size for ceratopsian babies. Therefore, if these three babes here are all that survived of one clutch of eggs, a large dinosaur like Arrhinoceratops may actually be coming out ahead of the game as opposed to how we think of modern mammal reproduction numbers and mortality. I like to think, though, that some of our dinosaurian friends may have evolved past eggs a bit additionally. Not all lizards and snakes today lay eggs, some have live births, and I see no reason why an Arrhinoceratops could not have had a live birth, tail first of course!, and that each one of these little pups could belong to one of the adults illustrated.