What you are seeing is referred to as 'tenting'. It is caused by lack of expansion joints. It is likely that the tile was set tight to the walls, and when it got warm and expanded, it had nowhere to go but up. For an experiment, take a piece of paper and lay it flat on the table. Near each end push the paper towards the opposite end slightly. You only have to move the paper a very small amount before it creates a bulge. Now, it could also be that it wasn't installed well - if they didn't use a large enough trowel and press the tile into the thinset, then you won't have good coverage. The gold standard is to achieve at least 90% coverage of thinset on the back of a floor tile, and more is better. If they spread too much thinset out before covering it with the tile, or it was too thin, or mixed too dry, or used beyond the pot life, then you may not get good adhesiion. Also, if it was walked on too soon after installation, you can have problems. If you have no expansion room, even if it is well adhered, you can get tenting, but in that case, it may crack the tile in the process rather than popping the whole thing loose. Expansion provisions are also an issue when you have a large area, or one that is unevenly heated because of large windows and sun exposure. Soft joints, or expansion joints may then be necessary in the middle of the floor as well as around the edges.
My guess is if you look, you'll find it was grouted tight to the wall, leaving it no room to expand. A good place for tiling help is www.johnbridge.com.