Drowned changes equipped item

I was swimming in the ocean randomly, and i saw a drowned with a tridents I killed one, but it didnt drop it. I then saw another one with a trident, and i hit it. I have knockback on my sword, and after i hit it, it changed its trident to a fishing rod.

i cant explain this with pictures but i have a clip. the clip is too big for attatching here, so if you want, you could tell me an email to send it to, if you are interested in seeing it.