How does System Information break down the Storage report?
Other is a catch-all by taking the drive's max capacity and subtracting the sum of all other counted file sizes. So, if your drive has corruption where many blocks are unavailable or lost, you will see large other "allocations". 

If the other space remains the same after running disk utility to verify and/or repair the volume then you can assume it's really files taking that space.

The categorization comes from spotlight indexing, so you could search here how to rebuild that index if you suspect bad metadata leading to an incorrect storage report. 

The simplest way to rebuild the metadata (spotlight) index is to simply add your hard drive to the spotlight privacy list in system preferences and subsequently remove it. The built-in help should have a guide if you're not sure how to refresh all spotlight data.