I never knew that but it is true.
https://en.wikipedia.org/wiki/List_of_massacres_in_Australia
It’s also true that Australia has more guns no than before the ban.
apparently the student misspoke, was talking about the 1996 massacre where 35 were shot dead. The gun ban went into effect because of that. And it does look like gun related “massacres” from that list, did decrease after that.