ummm all leds blink. always have always will, I'm not even sure a LED can be on constantly, if you look at the rear lights of a car in front of you that's LED, when you look left and right instead of leaving a streak, it will leave dots in your vision. so I'm pretty sure the draw was calculated with the refresh rate of the LED in mind.
Uh... no it wasn't calculated with that in mind. His calculation clearly uses a constant current draw value, which is highly inaccurate since the duty cycle of the PWM signal isn't accounted for.
The flicker you see on LED vehicle lights are the same concept. They control the PWM signal going to the LEDs to minimize the current draw from the battery. That's the major advantage of using LEDs...
So as I said before, any smart designer is going to manipulate the power signal for the LEDs to minimize the cumulative current draw.