|At the bottom of windshield fluid reservoir, there is a pump with a hose coming out leading to a Y spliter where two hoses connecting to nuzzles. Premium cars have a level sensor normally affixed to the top of the reservoir.
I am not sure how old your car is and what make/model is. I tend to believe that it's very rare they would touch the bottom hose to do regular services; rather, they would check the level from top and fill it up to the proper level if it's low. AND, noramlly a reputable shop or dealers won't do small tricks attempting to make couple of ten dollars by risking their reputations - they are in business, their reputation is more important than a small amount of quick money.
It might just be a coincident on the timing, or unknowingly they made the bottom hose loose. If doublt, don't go to the same dealer for future services.
** By the way, windshield fluid is very cheap from parts stores, less than $2/gallon. Don't add just "water" into it as you did.