Agreed - esp if you have had to foot the bill. Good job though it had been discovered and fixed as it was - you might have been driving at speed and had to have hit the brakes suddenly. That might have been a more costly and/or possibly more serious?
If the nails fell off a vehicle travelling in the opposite direction to you say at 30 mph and you were travelling at the same speed they could have bounced up off the road and hit your tyre.
The impact speed would be close to the equivalent of the nails hitting a stationary object at close to 60 mph - sufficient to embed them partially, at least, in the tyre. They would have been pushed in further as soon as your wheel completed the next rotation - just like banging them in with a hammer.
It has been demonstrated that at the right wind speed (e.g during a hurricane), a single sheet of paper has been blown "edge on" into a tree and was later found embedded several inches deep.