I am going to try to explain it better...
The CPU sends 32 ones and zeros per clock cycle, which is transported at 800 Mhz.
When the CPU is processing at 64-bit, it will send 64 ones and zeros per clock cycle at 800 Mhz. Considering in the end it will be transporting double the data, they say that it is transporting as if it were 1600 Mhz. However, the actual frequency is still 800 Mhz.
I don't know if I was able to clear this up more... If you have any questions, just let me know!