Actually, I didn't see any sort of auto start - check your owners manual. I found this online under "Timer Mode" - it sounds possible that this is what happened (you can always wait 3 hours and see if it does it again..haha):
By pressing the remote and buttons the parking
lights will flash 4 times and then start the vehicle and run for the
set duration. The remote start can be shut off by the transmitter
by pressing the remote start button and remain in timer
mode, but if any other shut down zones or the ignition becomes
active the timer mode will cancel.
1. Press Timer mode buttons.
2. The vehicle will confirm with 4 parking light flashes.
3. A 1-second delay will start.
4. The system will start the car and will run for the specified
duration, unless shut down by the remote start button . If
shut down with the remote start button the
system will remain in timer mode.
5. The system will start every 3 hours until canceled by the
The system will start every 3 hours until canceled by the
brake, hood, or neutral safety shut-down wires.
To exit timer mode, turn the ignition switch on any time the
engine is running. The parking lights will flash 4 times, indicating
timer mode has been exited.