In one of the snapshots, the Piglin mob moved very quickly, at the time of the attack on the player. The same thing happens in release 1.16.1
Linked issues
Comments 2
https://bugs.mojang.com/browse/MC-175296?focusedCommentId=654645&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-654645
The current speed, as per this comment, is intended.
Fast while doing what?