Drawing the map is multiple API calls. And interacting with the map uses additional API calls.
I opened the Inspector (in Firefox here), and you can see a ton of calls to maps.google.com - see all the file calls vt?pb...
- each one is a block of the map background.

And then, as you drag the map around, zoom, etc, it's making additional calls to get the portions of the map it doesn't have. And you can see them pop-up in the inspector.
So, a bunch of calls to draw the map, and more as you change your view of the map.
You could try the static image map {{ craft.smartMap.img(locations, options) }}
instead of the standard {{ craft.smartMap.map(locations, options) }}
Alternative ideas, disable 'zoomable' and/or 'scrollable' in your map settings (more about those options here) - less interaction = less api calls.
The static map loads a lot less API resources, but takes a longer to generate (and just isn't as good).