You can't fill-up the disk by making empty files - the disk will still have plenty of space for new files. But yes, you can exhaust the filesystem's finite supply of free inodes - at which point you can't create new files (even though your disk - as far used space go - are practically empty). It's just the filesystem's list of inodes that's all been used, not the disk... so the filesystem is full, while the disk is practically empty. The inode-table use space on the disk, but the table doesn't grow when you add files - just as a sheet of paper doesn't grow when you write on it's lines.

(an answer-in-a-comment by Baard Kopperud)