ender man acting weird

I was caving on my survival world then i saw a ender man i did not look at him. i started to sneak up on him hand when i hit him with my fire aspect diamond sword instead of the ender man freaking out and teliporting all over. he went insane and started to rapidly attack me. I was able to kill him quick but he did not do what they normally do. is this a new feature or is it a bug. so confused