"In college, my roommate was OBSESSED with Dairy Queen. So, I photoshopped screenshots of our school’s online news articles from Facebook saying a Dairy Queen was opening near us. She took it very seriously and started telling family and friends. After a few weeks, we sat her down and told her it was fake. She cried because she was so disappointed."
If it is really old and rusted pipes it can happen randomly, but typicaly after peaking pressure that will rattle the dirt in the pipes loose. Reconstruction where the pipes are knocked can also do this.
I don't think mom actually immediately thought of the exact cause, people...
She just thought something was obviously wrong which was the whole point. Best to move on, future plumbers.