From my experience with wireless cameras I have found that interference can come from passing cars which are using a similar wireless device which has a frequency close to yours. Also certain buildings automatic door openers can cause interference depending on the type of camera you are using and the type of sensors the door has. Some cheaper back up cameras operate on bluetooth, and are subject to many other devices transmitted energy.
The other factor in the design of the camera is whether it transmits in analog or digital. Think of the old comparison of FM vs AM radios.....where lightening storms almost make AM radio unusable whereas the FM radios are unaffected. Analog vs digital transmission of signals is very similar to that comparison. Digital is better.
When someone uses a term such as "outrunning the signal", it's just an uneducated description of interference of the signal. Besides, if you start talking technically to a lot of folks their eyes glaze over and they just nod and say uh-huh. So maybe outrunning the signal is an adequate response in most situations.