On this matrix, 128 RGB pixels switched on at the same time, each pixel contains a 3 LEDs. Taking the typical current for an LED of about 0.02A, we get
128 x 3 x 0.02A = 7.68A
I assume that the 3A indicated on the site is "typical consumption" and not the maximum, this figure calculated on the basis that the panel will not be completely illuminated.
Also, specifications on store websites are often copied for similar products, without realizing that the numbers may be different.
PS
But of course, these are my assumptions, nothing more.