Disney came up with the standard for locations with more than one park (aka resort), to calculate per-guest spending, hotel stay percentages, etc. Only the first park of the day counts in the official daily attendance. Of course, Disney also does track the secondary numbers, they just made the main number to reflect how many folks visited the resort in a single day.
So someone who enters Disneyland first, then park hops to DCA, that counts as a Disneyland visit, of course, switch it around, and it counts as DCA. Over the last two decades, Disney has done a lot of tricks to have folks enter DCA first, or at least try to.
Same for Knott's, the TEA number reflects one or the other, while internally it can count as 2, heck, you could say some visited 4 different parts in the same day, inflating the number they can claim.
That is why TEA sticks with the Disney view of one visitor, one Hotel Room, and one park per day.