Whilst he is likely full of shit, your link is really not saying anything either. Specifically:
"Mass murder has generally been defined as the unlawful killing of four or more individuals, excluding the perpetrator(s), within one event, in one location. In 2013, the US Congress proposed the alternative parameter of three or more victims (Douglas, Burgess, Burgess, & Ressler, 2012; Krouse & Richardson, 2015)."
The term 'mass shooter' when used colloquially is not the same as used in the research. Many of these 'mass shootings' are going to be perpetrated by gang violence usually against other gangs. The public discourse, however, on the subject does not care or have any connection with that type of shooting. What people are generally talking about when they refer to a mass shooting are the major news stories of single shooters gunning down innocents for what seems like no reason or because of some extremist views such as the aurora shooting, the recent nightclub shooting or the Vegas shooter. These 2 types of shooting are fundamentally different and require different approaches, have different underlying causes and bear no resemblance to each other in any way shape or form.
This is also an international analysis. I am somewhat incredulous that we can compare mass violence like this between very different nations. For instance, how many of these mass shootings were in nations under political upheaval? It would be nonsensical to include them in an analysis of mass shootings and then apply that analyses to any US shootings. They simple do not have any underlying connections that would inform us of anything useful.