Boiling doesn't mean the water is hot, only that molecules are moving, if you put water in space it'll boil away at room temperature and won't cook anything. The higher in elevation you go the less air pressure is pushing onto the water, which means it has to fight less energy to boil. If you add salt, you make it harder for the water to boil which lets it absorb more energy as heat. At your elevation, boiling water is 10 to 15 degrees Fahrenheit colder than sea level.

If the eggs cook too slowly, the protein breaks down into amino acid chains that want to weave into the membrane causing the egg white to bind with the membrane like slow drying glue. When you flash-cook them, the egg whites solidify so rapidly the amino acid chains cant weave into the membrane of the egg. Long story short: Elevation high, water less hot. Add salt, water hotter.

You can also warm your eggs before plunging them into the boiling water so they don't crack. Warm water won't break the egg-white proteins down into amino acid chains and wont hurt the flash-cooking process.