Why are there 5 or 6 threads exposed on the left stop bolt and none on the right? There doesn't look like there are any threads beyond the lock nut at all, which isn't right.
I think the mechanic had to cut the right stop bolt short, because at full-length he couldn't get it inside the horn to start the thread. Apparently there was enough room on the left side.
Even at shortened length, there's enough of the bolt inside the locknut to keep it secured. Plus, the nutplate that the bolt is threaded through is enough to keep it from going anywhere.