@kilisloe He compressed mana until it took a solid form, the magic stone. It doesn't take knowledge of the process of diamond forming to think of trying to make mana radiating stones out of mana, I'd say. If you always needed to know everything beforehand before trying stuff, we would still be living in caves and fire gained from natural wildfires would be our highest form of technology. We have had that modern way of thinking among us since the scientific revolution from the late renaissance (or at least Europe had, Japan not yet for a few centuries more). If you look at the society in this manga, it looks more developed than that, sans firearms, naturally (at least I think guns weren't there in this story).
You are forgetting he's the dude with no common sense, like people around him continuously think. Of course he would mess with antimatter if it happened to interest him.
Well, you should just ignore my complaints from now on. It's not even so much this series' fault but the fault of an overdose of OP MC isekai in general. It would be nice to get, every now and then, a series where the MC needs to start from closer to the bottom with no haxor skills, in a world where the MC isn't automatically the best.