As mentioned: on what; where; what type corrosion; etc, etc. Some is treatable. Some is repairable. And some requires part replacement. Pictures? Aircraft?
Corrosion X is the better product. Most Part 135 helicopter ops in the Gulf of Mexico have long switched to Corr X as it performs better than 50. The key is applying it as a mist. And as an FYI, corrosion is not all about whether it's a rainy/humid environment. Various air pollutants (i.e., urban areas) are just as detrimental on aluminum and can cause corrosion also. Keeping the aircraft clean and using some sort of corrosion preventative plan usually keeps you ahead of the game.
Perhaps they did a spot treatment of the corrosion and planned to watch it? Can't really comment without more info. However, in some cases, people view light surface corrosion in the AlClad coating of the aluminum as normal wear and tear vs something out of the ordinary. But corrosion never goes away on its own so a complete corrosion control plan is always the best practice in my book regardless of where the plane resides. Here's some additional reading that will give you more background: