We’ll it broke when you re-installed the screw. That should not happen no matter how many times it was done. Possible factory defect? That was my thought at the time.
If the pilot hole for the screw was not long enough, driving the screw in tighter would make the screw act like a wedge.
You can see the screw hole was placed very near the toe of the stock, a bad mechanical choice.
If the screw was "cross-threaded" and driven in at an angle, that could contribute. Or not putting a little wax on the screw to lubricate it. Or the pilot hole was too small a diameter.
But the user should be able to take the butt plate off and on without doing that. But now the thing is to get it fixed.
If the OP is not comfortable with this operation, any competent gunsmith can do a basic repair that may not be invisible but will be strong... but the customer should ask what to have done so it won't happen again.