Nautilus has a default fallback action if the partition on the disk does not have a label: it says "{FILESIZE} Volume" for it to be somewhat more useful for the end-user. However, this doesn't change the back-end mounting behavior it uses which is based on the UUID of the partition. (This is only the case if you do not have a label on the disk partition for it to display. And not all filesystem types support disk labels, depending on the age of the filesystem type)
Behind-the-scenes, however, this is actually a case where the system at its base is using the unique identifier of the disk as the mount-point folder name.
Consider this example - this is my existing hard drive and disk ID data from blkid on the command line:
$ blkid
/dev/sda1: LABEL="System Reserved" UUID="C63884F13884E233" TYPE="ntfs" PARTUUID="1f35ad56-01"
/dev/sda2: UUID="805C879B5C878A9C" TYPE="ntfs" PARTUUID="1f35ad56-02"
/dev/sda3: LABEL="DATASTORE" UUID="1E3AD5A957140669" TYPE="ntfs" PARTUUID="1f35ad56-03"
/dev/sda5: UUID="84445130-00d6-4cba-9d1c-34b9e04c499a" TYPE="ext4" PARTUUID="1f35ad56-05"
/dev/sda6: UUID="08610b3f-1bc6-4f2b-be71-f0317415f96f" TYPE="swap" PARTUUID="1f35ad56-06"
/dev/sdb1: UUID="0B43-D39A" TYPE="vfat" PARTUUID="137296b7-01"
There is a total of 5 partitions. /dev/sdb1 here is a USB stick jacked into my computer.
Notice the UUID field. This is the unique identifier of the device / drive itself. For hard disk partitions this is a long-form UUID string. Let's say that I am mounting /dev/sda2, which is my Windows dual-boot partition. The Windows disk partition does not have a "LABEL" field. So the system doesn't know what to use for the label in the mountpoint or in Nautilus. As a result, it creates a mount point for my user at /home/teward/805C879B5C878A9C which is based on the unique identifier, and displays the filesize in the 'label' on Nautilus ("822GB Volume" specifically is the label Nautilus sets, which is the approximate size of that partition). The UUID is usually always unique and therefore is a 'safe' way to create the mount point that won't conflict with any other similarly-named drives/volumes with similar labels being mounted simultaneously. (This is the default behavior if no drive labels are at play, and if there are duplicate drive labels it appends 1, 2, etc. to whatever the mountpoint is).
TL;DR: If you set a label on the partition/drive, it will properly use that label name (unless a conflict exists) in the path for the mount point as well as in Nautilus. If you don't, it uses the partition/drive uuid for the mount point and the volume size of that partition/drive in the Nautilus label.
To set a label on a given drive, you might want to install gparted, navigate to the drive that has the unlabeled partition, right click the partition, choose "Label File System", and then set the filesystem label. Note this is usually a short string, and for older filesystem formats you can't use more than 8 or 10 characters.
