My interpretation of all this is that the mechanic is trying to tell you that by lowering the car, you have now setup a situation where you will have negative camber gain as the suspension compresses. I looked at this on my car a while ago, but do not remember the details. At stock ride height, I think I recall the suspension produces mild positive camber gain before going negative. On a lowered car, the suspension starts out with negative camber gain. This is not necessarily bad. You want some negative gain so the tires lean into a turn. Some cars have been purposely modified to do this. You don't want too much though. This should definitely not be a problem with any of the lowering springs available on the market, so don't worry about it.