According to minecraft :Piglins arms are now behaving more like the players arms, and less like the zombies arms MCPE-74089(1.16.20.50)

This means that zombified mobs like zombie and zombified piglins should have this arms :

https://1drv.ms/v/s!Av8v0VZb-r4rgXm-wMwx9SXH6brr?e=xH0gY3

In the video there's a piglin (1.16 ) who has the zombie arms is actually a bug he shouldn’t have this zombies should