The Stampeders have had big attendance records like that, including some in the early 90s when Doug Flutie was QB and the team was winning.
You or the people you're talking to may be conflating it with the Hub Oil explosion that happened in 1999 which was a pretty significant event locally. IIRC, there were only a few workers at the facility who were killed, but it was a very memorable event if you lived in the city around that time.
I think this is a nothingburger.
Calgary was hosting the Grey Cup in 2000, so the stadium would've been expanded to accommodate seating.
There are photographs of the game here:
https://www.cpimages.ca/archive/STAMPEDERS-ALOUETTES-2RLPN4X03U5H.html
Mark Stephen, who was the radio voice for the Stampeders, recalled the game in a Facebook post:
https://www.facebook.com/markonfoot...on-the-verge-of-becoming-th/3254210574825639/
The other thing that might be getting conflated in people's heads were the talk about renovating/updating Foothills Stadium, a baseball stadium right next to McMahon Stadium that ultimately led to the minor league baseball team leaving around that time period.