1) Do you have 2 or 4 processor sockets populated?
2) Do all processors have DDR3-1333 memory installed? So every processors use the same memory configuration?
In case you have 4 processor sockets populated, and every processors use the same DDR3-1333 memory configuration, that would mean you've got 16 memory channels total, each running at DDR3-1333 speed, which would mean a total memory bandwidth of 166.6 GBytes/sec. Hence the results could well be accurate
The confusion may come from the fact that AIDA64 (the main application itself) only supports up to 32 processor threads, so it cannot show you all processors on the Cache & Memory Benchmark Panel. However, the multi-threaded memory benchmarks support up to 64 processor threads, so it can utilize all 48 processing threads you've got in your system (if you have all 4 processor sockets populated, each with a 12-core Magny-Cours CPU).