This was on a single player server with most updated 1.15

So, I was on a sandy beach and saw a light below, and found an ocean ruin. I used a stone pickaxe to mine a sea lantern, and I quickly swam back to shore to make sure I got it, but when I looked in my inventory, I had an sea lantern, AND 2 prismarine shards AND 1 of those circle prismarine thingys, I think it was called a prismarine crystal. I never went into the ocean before, only that one time. Why is this glitch happening, and did mojang fix it in 1.16.5?
Sorry this isn't a confirmed error in 1.16, but did they fix it?