Chances are, Wocka is right.... I've search the RAVE manual, but found nothing close to it. I would go back to the garage and ask if they had a bolt missing from someones car recently. if they say no, ask them where the offending item came from on yours, stress your concern and ask then to do a full inspection to put your mind at ease.
an honest garage would tell you they were working on something and looked for ages for a missing bolt.... or tell you to leave the car while they investigate. a dishonest garage would deny all knowledge of it...
But to ask... you would probably need to do it in a jokey type friendly manner - so they don't do the "silence" trick on you.