Getting swarmed with baby pigmen spider jockey???

I was in the overworld when I was heading to my treehouse base when I heard something crawling, so being my naturally curious i went to investigate, only to find a super fast dimond sworded baby pigmen riding a spider at super speed, this is freaky and I hope wasn't an intentional implement because these things are brutal it kept killing me and after i die then click repawn it FOLLOWS ME! please tell me this was a one time glitch or something cuz none of it makes sense.