It sounds like all he did is blow some air around drying out the moisture without cleaning thinking thats all that was needed.
I would first ask them what did they do. The more info they tell you the better. I would hold off telling them the system died until they tell you what they did in detail. Come up with some excuse like it was your uncles system and he wanted to know what was done. Tell us what they say as detailed as possible as well as how much they charged you. Then we can figure out if you should send it back.
The issue here is if there was still some moisture it could have continued to corrode things. Coffee (depending on how you like it) will have acids, sugars as well as fats &proteins (milk/cream). In addition the water that was used to brew the coffee will have minerals and salts which are all corrosive.
Locating the areas the spill happened is important as these areas need to first get fully cleaned. The ideal solvent is water! '''Not tap water but distilled water (pure H2O)''' I know a lot of people will disagree but it’s the best here.
Now using cotton swabs (Q-Tips) or surgical sponges wipe down the areas as if needed use a soft tooth brush to go over any stained areas (making sure nothing is left behind). Even still you can’t leave the distilled water on the parts here we are going to use a high grade isopropyl alcohol (85% or better) to wipe the same areas. The alcohol has the infinity to draw out the water as a dryer and it will also evaporate cleanly.
Thats what they should have done. Even still its possible some parts are beyond help or just impossible to clean. These parts would have needed to be replaced.