The assumption that the brakes were reinstalled incorrectly is not supported by the statements of fact made by the OP. The fact that he traveled 6,000 miles after servicing the bearings makes that scenario very unlikely.
Improperly installed brakes will almost certainly not travel 6,000 miles before manifesting themselves. A deployed drum brake will boil the grease out of the hub in very short order. It will also scrub the friction lining off rather quickly. There would be no friction material (or metal backing, for that matter) left after just a few dozen miles.
A spring broke, the shoe engaged the drum and heated the grease sufficiently that it ran out. Bearing failure occurred shortly thereafter. A simple failure of a piece of (Chinese) spring steel and a lighter wallet. No need to point fingers or assign blame. IMHO