They are only counted once. Most don't leave the airport, and aren't directly involved in generating tourism, but in some ways they are indirectly involved in generating tourism, as they are a big part of the reason for all the direct US/Overseas flights. Those direct flights probably have some affect on tourism to Calgary, mostly Banff, how much I don't know, it's probably not huge numbers, but it helps.
Not true; the first table even says explicitly that these are enplaned and deplaned passenger statistics.
This means that a passenger is counted if they get on a plane or if they get off a plane. So a visitor from Portland is counted once the day they arrive as a deplaned passenger and once the day they leave as an enplaned passenger. Even worse, a connecting passenger (assuming a symmetrical booking) is counted four times; if the Portlandian was actually a connecting passenger heading to Edmonton, they'd be counted the day they left home as a deplaned passenger PDX->YYC and as an enplaned passenger YYC-> YEG, and then the day they returned home as a deplaned passenger YEG->YYC and as an enplaned passenger YYC->PDX. Four counts on the table, and they never leave the airport.
(I should note that this is the standard for the airline industry, not something shady being done by YYC -- yes, it inflates the count of passengers relative to naive expectations, but everybody does it and nobody wants to be the one to cut their volumes in half or more.)
The financial reports and quarterly management statements
here (select by year) have the actual detail. From the 2023 annual report:
Look at the top two rows, and the second bolded column (2023 year total). 18.5 million E&D passengers is actually 6 million enplaned passengers from Calgary, another ~3.2 million connecting passengers enplaning (making 9.2 million total enplaning, 34.6% of which are connecting) and presumably very close to the same in reverse for deplaning passengers. For each headline E&D passenger in the 18.5 million, there's about 0.325 true local enplaning passenger.
(I'll note that if there's 18.5 million total pax and 9.2 million enplaning that means 9.3 million deplaning; while enplaning and deplaning is mostly symmetrical it doesn't have to be perfectly. Someone moving here and flying will deplane once, and then we would expect their next trip (e.g. to visit their former home) to have both an enplane and a deplane. Calgary CMA gained about 0.1 million people in 2023.)
This ratio is reasonably consistent over time; it was 0.315 in 2022 (4548.5/14452.1). Here's the ratio over time:
The operating detail is not reported prior to the 2021 financial report (which includes both 2020 and 2019 operating information), however in the previous financial reports, the airport improvement fee revenue is reported; it's a fixed amount ($30 at the time) per passenger and applied to all originating passengers (i.e. at initial enplaning), so a very good estimate of local enplanements can be made. While the chart looks like a lot of change, note the axis; the total range is 6 percentage points, but excluding 2020, the range is about 0.02. The higher the ratio, the fewer connecting passengers there are.