Sounds like a fairly typical experience for just about all of us. You didn't panic and fixed the problem. You spent the day on the water and the boat still floats so it was a good day. We've all been there.
Be sure to check every place the boat yard could have accessed/modified during any work they did. This issue could have cost me my boat.
Better yet, do your own work unless the tools are too specialized or expensive (I can't afford a TraveLift). Often times, yard personnel are less experienced than the owner. A great example is painting a bottom - the least experienced guy (i.e., the one making minimum wage) does the work.