Random frozen Blue wither skull projectile

I was walking around my base killing mob (creepers, skeletons, zombies, exc.) and i noticed what looked like an Ender chest in the sky. Knowing i hadn't place it there I jumped stacked up to it out of curiosity and when I got up there I found that it was a blue projectile skull from a wither. I do use optifine but that is it. I had done a wither fight about an hour before this. This fight was about 300 blocks away though and my base wasn't loaded at the time as far as I know. When I logged out it disappeared

I have no idea how this happened

I hope the screenshots help