32 shootings in private homes where-in the victims were related to or romantically linked to the killer, who (in at least 23 of those instances) took their own life during the shoot out. Kind of hard to argue that a mass shooting of that nature is at all similar to the mass shootings comparable to the knife attack we're discussing in this thread. Hell, I would argue that ANY mass shooting in a home is an unequal comparison to other mass shootings simply based upon how people view "home" vs. "public" (i.e. inherently safe vs. inherently risky). But for the sake of argument, I'll limit it solely to the domestic violence encounters.
Then, you have 23 shootings that took place either inside of or immediately outside of bars. In MOST states, it is illegal to conceal or open carry in a bar. It would appear your link is arguing that since the area outside of the bar is NOT the bar, that any shootings occurring their would fall into the larger category of "legal carry" scenarios. I'd have to say that's a little dishonest (if that's the assumption), as most (if not all) of those shootings resulted from altercations between bar patrons, including those which ended up outside before shots were fired.
So you have the 23 bar shootings, plus the schools shootings. I didn't bother looking up which states (if any) allow you to legally carry a weapon (concealed or open) inside of a bar.
In any case, I guess I'm questioning the validity of your link, considering that little blurb is entirely un-cited.
If we're to assume 56 is the magic number of mass shootings (if your link is accurate in THAT regard), then close to half occurred in areas that are legal "gun free" zones, or immediately outside of those areas (i.e. outside of a bar after a spill-over altercation moves outside).