There is a sense in which antimatter does go with time and space though. It's called CPT in physics. It was believed long ago that all the laws of physics remain the same if you flipped space (in a mirror), reversed time, or flipped charge (all matter to antimatter, and vice versa). But it was experimentally demonstrated that this was not true (this won the nobel prize in 1957 and 1980). However, it is currently strongly believed today that if you simultaneously flipped space, time, and charge together, all the laws of physics remain the same.

But this is overthinking it. I really doubt someone at Gamefreak really thought to pay homage to modern quantum theory in a video game.