If you look at the previous picture, it's bedrock. So they don't need a foundation. Foundations are dug in Canada/Quebec to get below the the ground which freezes. It has to be because freeze/thaw cycle would crack the walls after a few years. But that only applies to actual soil. Here, the bedrock wont move much, if at all. So a simple slab is enough. Primary schools don't all have a basement. Mine didn't (built in brutalist style from in the 60's). When they built a condo block next to it, I can confirm the bedrock was like 2 feets from the surface. Same as this site. They used dynamite and it was pretty cool for a 7 years old to see this from the edges of the playground.
I suggest this video: