The exact thing happened to a neighbor when they were having the final inspection on the condo they sold!
The water was off and the Realtor turned it back on from the outside shutoff.
The downstairs neighbor was sitting in his Livingroom and heard "his shower running".
When he went to investigate he saw water running out of the can light over his tub. he went to the upstairs unit to see what they were doing and the people in there had no idea anything was wrong. They only heard a rumbling noise in a wall of the bathroom when they went to investigate.
What happened was a CPVC fitting was never glued and came apart with the sudden pressure spike of the water turning on. So what happened in your mother's house is not uncommon. Investigation will be needed to find the issue, ( weak pipe, bad connection, etc.) This in no way would be your mother's or the handyman's fault.