Lightroom version: 6.0 
Windows 10 Home 64 Version 1067 (latest)
So, I just imported (add) video and photo files to lightroom from an internal hard drive.
I happened to have a thumb drive in the computer at the same time I clicked "Import".
Now my C drive with operating system and lightroom catalog is 155GB bigger.
Looking for hidden files, I discovered C:\Users\Gustavo_Std\AppData\Local\Adobe\Lightroom\Caches\Video is the culprit.
Lightroom created cfa and pek files FROM the thumbdrive that was inserted in the computer but that i DID NOT CHOOSE TO IMPORT from.
I happened to have many movies in there. So now, guess what? I have cfa and pek movie files in the lightroom video cache folder that I did not import.
Searching the lightroom catalog does now show the movies. They were not chosen for import.
Clicking clear video cache in Lightroom preferences does not erase these phantom files.
Looking around the forum this problem has been around for years (see below forum link)!
Can anybody please tell me how to clear the C:\Users\Gustavo_Std\AppData\Local\Adobe\Lightroom\Caches\Video folder without breaking lightroom?
What folder should I delete from?
If I only delete the cache, will this brake databases references?`
For everyone who struggles with this bug, you can use this as a workaround:
Just change the directory from the Downloads folder to:
"C:\Users\YOURUSERNAME\AppData\Local\Adobe\Lightroom\Caches\Video\Media Cache Files\"
Also, change the timeframe in the .bat file from -30 to -0, that will delete all the files in the folder, not just the files older than 30 days.