Question about setting the next pixel value to zeros in DMA_TransferHalfHandler

[yp05327]

I have a question about the code here: https://github.com/hubmartin/WS2812B_STM32F4/blob/0e47916345becbebc0dad0df188d80d8b8a7991d/Src/ws2812b/ws2812b.c#L315 The first parameter of ws2812b_set_pixel is led channel, so the code above should set all channels as the following but not only channel 0?

for( i = 0; i < WS2812_BUFFER_COUNT; i++ )
{
    ws2812b_set_pixel(i, 0, 0, 0, 0);
}