This is not true. The second press, as Murky notes, is just a confirmation.
Here is what the manual says:
"How to Arm the System
1. Close the windows and the moonroof securely.
2. Press the push button start off.
3. Make sure the hood, the doors, and the liftgate are closed.
4. Press the lock button on the transmitter or lock the driver's door from the outside with the auxiliary key.
The hazard warning lights will flash once.
The following method will also arm the theft-deterrent system: Press the door-lock switch while
any door is open and then close all of the doors.
(With the advanced keyless function)
Press a request switch.
The security indicator light in the instrument panel flashes twice per second for 20 seconds.
Refer to Warning/Indicator Lights on .
5. After 20 seconds, the system is fully armed.
NOTE
• The theft deterrent system can also be armed by activating the auto relock function with all the doors, the liftgate and the hood closed.
• The system will disarm if one of the following operations takes place within 20 seconds after pressing the lock button:
• Unlocking a door.
• Any door or the liftgate is opened.
• The hood is opened.
• The ignition is switched on.
• (With the advanced keyless function) Press the electric liftgate opener while the key is being carried.
To rearm the system, do the arming procedure again.
• When the doors are locked by pressing the lock button on the transmitter or using the auxiliary key while the theft-deterrent system is armed, the hazard warning lights will flash once to indicate that the system is armed."