If there were beings made of antimatter in an antimatter galaxy, their understanding of the universe would be fundamentally different from ours due to the opposite properties of antimatter compared to ordinary matter. In such a scenario, their version of "ordinary matter" would be composed of particles of antimatter, and they would consider it as the norm.
It's reasonable to assume that they would have a similar concept of "antimatter" as we do, but from their perspective, it would be the matter composed of particles with properties opposite to their "ordinary matter." They would likely have discussions and studies about the properties, behavior, and interactions of antimatter within their antimatter-based civilization.
The creation of matter would indeed be as challenging for them as the creation of antimatter is for us. Antimatter and matter are known to annihilate each other upon contact, releasing a large amount of energy. Similarly, matter and antimatter creation processes require the conversion of energy into particles. So, from the perspective of beings in an antimatter galaxy, creating matter would involve significant energy input and technological complexities, just as creating antimatter is challenging for us.
However, it's important to note that our understanding of antimatter and its behavior is currently limited, and we have not yet encountered an antimatter-based civilization or an antimatter galaxy. Speculations about the nature and behavior of such civilizations are based on theoretical considerations and hypothetical scenarios. Further scientific research and discoveries would be necessary to provide a more comprehensive understanding of antimatter and its potential implications in the universe.