According to this forum post, negative exclusion wasn’t added until restic v0.13.0 (release notes, issue, PR). So it seems you will need to update the restic version in the container if you want to make use of them.
I had a look, but can’t see any negative exclusions in the docs for 0.9.6, only for more recent releases. Could you share where you saw the negative exclusions in the docs?