That though was not offered and the original files have since been erased.
Most likely just the directory that points to the file data.
A common misconception amongst those who wish data to be beyond scrutiny.
There is quite a good selection of forensic software, both free and commercial, that's built to handle the often proprietary file systems of many brands of NVR.
Is that something you have explored, or are familiar with?
A few months back I bought a Hikvision NVR that still had the HDDs installed.
The seller had 'formatted' the HDDs via the NVR menu system and they were apparently blank.
Not so when processed via some forensic software.
"It's a Hikvision structured file system, here is a named and dated list of 10s of thousands of video files, which do you want to extract?"