If nothing is loose or "broken" then my gut feeling is:

With all the steep inclines and bumping and jarring ( also the pressure difference with altitude ) the coolent simply "sloshed" out of the reservoir cap. Maybe the cap got loose, or exceeded the 17psi rating.
If it does not happen again, then don't worry about it.

Of interesting note, today I took mine up I70 over the divide with 3 adults and all the ski gear incl. roof ski rack. Had to run at 4000 RPM for like 30 minutes continuous. Even though outside temperatures were about 28-30 degrees and it was snowing, my coolent got hot also. About 200 degrees. Not dangerous, but much warmer than the Standard Op. Temp. of 184 degrees.

When I went through Vegas in July with 114 degree ambient temps and Max. A/C on, the car never exceeded 190'F.

???