The Tesla map tiles are from Google but the implementation of the app sucks. It doesn't preload tiles along your route so if you go out of mobile coverage it just draws blank rectangles which is hideous. There are many other defects.
It gets improved over time with frequent updates though, including new map data. And I don't know how stale your knowledge is on this, so I wouldn't be so sure this is a problem. People tend to repeat very old information a lot about Tesla, when reality has already moved on. I haven't had a problem with blank tiles in the last year or so and I've been plenty of places with low/no coverage.
