A mass shooting is an energy shooting divided by the speed of light squared.
This was not a mass shooting. The perp killed his ex and a few others, then turned the gun on himself.
Back in 1980 it was if there were four or more deaths. In 2012 they changed it (U.S. Statute) to three deaths or more. Some “gun safety” groups have it as four or more people shot, even if they survive. That of course promotes their idea that “gun violence” has increased and that more needs to be done to ban guns.