When on a lead, axolotls on land will swim as if in the water. If unleaded, axolotls will go back to their original walking speed & animation.

Steps to reproduce:
Run 1.17.1 Optifine

Set gamemode to Creative

Spawn an axolotl in a body of water

Use a lead to pull it out of the water 

Unlead it when on land after observing it "swim" on land