I'm assuming you are asking why you see the described behavior. The answer is that the receiver knows nothing about the LNB other than what you tell it.
The LNB is responsible for shifting the higher frequency bands (~5GHz for C, ~10GHz for Ku) to a standard lower frequency band called the L band (~1-2GHz). Every LNB you will encounter shifts to this L band, regardless of what frequency is being received. And every receiver only tunes the L band.
The receiver, as a matter of convenience to human eyes, simply computes the original frequency. If you provide incorrect information about the LNB (as you did in this case), it will display the wrong frequency. What physically is going on is you are truly receiving C band, and the receiver is using the wrong equation to tell you what frequency you are tuned to.
I think this all speaks to your second question, too, if your question there was about tuning capability. Since both C and Ku band are shifted to the same L-band, and that tuner tunes L band, there really isn't a problem with capability. If your question is about switching between the two, you have several options available. I'm not familiar with that particular receiver, but it has an oldness ring to it. I might guess it doesn't do DiSEqC. A manual switch might save you from having to disconnect and reconnect coax each time, but they are not the best thing to use given the high frequency. It probably has a 0-12V output for polarity control.. if a coax switch doesn't exist that can use the 12V as an input, something homebrew can be whipped up.
