The following post gives an example of how to use the delete-rockon script which is intended for just this kind of situation, ie the accidental deletion of docker associated snapshots:
visiting that thread directly will give better formatting of the info there.
We recognise that not surfacing/indicating the rock-on/docker related snapshots is a usability failure on Rockstor’s part and we have a couple of GitHub issues to address this that are in turn referenced in the following forum post: