I am sure that in 5 minutes it didn't delete all my data?
Agree. That would take hours.
I don't know that box, and unfortunately JBOD has at least 2 meanings. It stands for 'Just a Bunch Of Disks', and in NAS world it can mean that all disks are used as seperate volumes, but it can also mean the volumes are glued together to one big volume. (Linear raid).
If the box generated a 2nd volume, there should be no problem. If it generated 1, bigger, volume, it either reformatted the new volume, or growed the filesystem on your original disk.
You'll have to look at the disks to see what actually happened. You'll need a Linux system for that. Any PC booted from a Linux Live USB-stick or -CD will do. Theoretically you can use the NAS itself (it runs Linux) but AFAIK it has no default shell access, and installing extra software is not recommended, at the moment.