Why is the partition mounted via "fromhd=..." rw?

[Albretch]

First I boot knoppix as:

knoppix64 init 2 no3d fromhd="/dev/sdc5"

then I see

$ mount | grep mnt-system
/dev/sdc5 on /mnt-system type ext4 (rw,relatime,block_validity,delalloc,barrier,user_ xattr,acl)

$ blkid | grep sdc5
/dev/sdc5: LABEL="KNPX771" UUID="54e317fe-73cf-4b1c-8b1f-dfc9b708b68a" TYPE="ext2" PARTUUID="591ef660-03"