Going through blocks

I was playing with my sister on a LAN world and I got a trident with riptide III on it. I used a  command to change it to rainy and I was flying. I got so fast the chunks didn't load and then I went down in to the void and died. Later I did again but this time I apparently flew into a mountain and I had to dig out. I did again to test in  survival In a mountain biome and I flew at level 64 (from an ocean) without dying when I stopped I was in a tree. All was done in creative.