Welcome to Mac-Forums..
Is this a Apple service center or some third party? That whole one drop of moisture thing sounds quite dumb..
The MBA tech specs state:
Operating temperature: 50° to 95° F (10° to 35° C)
Relative humidity: 0% to 90% noncondensing
Operating altitude: tested up to 10,000 feet
Those are rated temps, does that mean that the MBA will stop working at 100° F? No, but you should try not to use it for too long under high temp situations. 0 to 90% humidity covers a VERY quite range and shouldn't be a problem.
If this is a Apple service center, they should be ashamed of themselves, if it's a third party service center they are making up BS..
Have them photograph the failure spot and tell you WHAT exactly it is. Then go to
http://ifixit.com and find the tear down of your MBA (based on year) and figure out what parts are around that area and see whats going on..