Hmmm, I'm thinking these "cameras" mentioned above may have been installed by a BMW dealership in your market or by a previous owner...but they didn't come off the assembly line with them. If they did, there would be cameras for the e53 in the BMW part database...and I can't seem find them.
For example, below is a simple search for "camera" using my 2006 e53 X5 versus a 2012 e70 X5 35d on three different online part database sites (realoem, bmwfans.info, and etk.cc). A reversing camera can be easily found in the BMW database for the e70 X5...but none appear for the e53 X5.
A BMW dealership can add-on a reversing camera if it's something common and popular in that market as an accessory...but it doesn't always mean that it comes from the factory that way. Just like Bluetooth telephony capability wasn't offered from the factory until Oct/2004. Up until then, there may have been aftermarket products that could be added, then BMW eventually offered BT ULF components in their accessory catalog as well so that some BMW models built prior to a 10/04 build date could update/install BT technology.
e53 X5 (VIN: LV2133):
- RealOEM.com - Part Search
- http://bmwfans.info/parts-catalog/E53/USA/X5_4.4i-N62/L-N/dec2005/search?s=camera
- https://www.etkbmw.com/bmw/EN/search...E4i+N62/USA/66
e70 X5 (VIN: L665930):
- RealOEM.com - Part Search
- Search result: camera
- https://www.etkbmw.com/bmw/EN/search...%252E5d/USA/66