bad /etc/fstab causes not recognicement of usb memories

I cannot be sure if it was happening since the installation. The issue is a wrong content of /etc/fstab

$ cat /etc/fstab
# /etc/fstab: static file system information.
#
# Use 'blkid -o value -s UUID' to print the universally unique identifier
# for a device; this may be used with UUID= as a more robust way to name
# devices that works even if disks are added and removed. See fstab(5).
#
#
proc /proc proc nodev,noexec,nosuid 0 0
/dev/sdb1 / ext4 relatime,errors=remount-ro 0 1
# /home was on /dev/sdb6 during installation
UUID=e876f719-98dd-45ee-b6e2-71b8280c6d80 /home xfs relatime 0 2
/dev/sdb5 none swap sw 0 0

The /dev/sdb1 was avoiding to automount the usb memories that were pluged in. However, the system mounted the second one. I don't understand how is mounted /dev/hda1 on /

$ mount
/dev/sda1 on / type ext4 (rw,commit=0,commit=0)
[...]

but it is and the OS is perfectly usable.

I solved the usb issue commenting the line. Since /dev/sda1 is mounted, I didn't add any line more for it.