More context would be good.
The screenshots in your first post are from hpe1, which uses ZFS (local-zfs storage).
The screenshot in your second post is from hpe2 and you say you set it up with ext4.
So do I understand correct, that hpe2 has no disks with ZFS at all, but the ARC-cache is nevertheless utilized?
Can you please post the output of zpool status
from hpe2?