I know its not much use now but even as a long time car owner I do not trust any tyre fitters or garages if a wheel has been off.
at a point soon after I will recheck the bolts and maybe (usually) have to slacken and then retighten the bolts to a more reasonable tightness(one which I could undo roadside with tools available)
they unfortunately have a nasty habbit of using air wrenches to fit bolts and I find theyre far too tight and would never get off again with the wrench in the boot(even I have an extendable wrenchin boot just incase).
also most tyre fitters have a habbit of using the air wrench on the locking wheel bolts , which can ruin the bolt head and the removal tool.
also just to clear up, in the photo of the brake disc I cant see any sheared bolts in the holes ?
I do see the 2 wheel alignment bolts screwed into the disc are still in place that is looking like a normal hub / disc with the wheel removed, apologies if there are bolts broke in the threaded holes but it doesn't look like it in the pic.
although its been a nasty incident for you , you have been uninjured this time and hopefully being less trusting may help you in a long life of car ownership.
I hope you get it sorted out quickly and not too costly, agree with your family if you go to the garage and explain whats happened you have a 50/50 chance they may accept responsibility and have some sort of insurance its got to be worth a try , not all garages will try to dodge reponsability.
and lastly when you find a good trustworthy place stick with them.