I am a mum who adopt baby led weaning for my kid. It turns out well, but sometimes i found chunk of veggies in his poo. Is it a sign that my baby didn't get enough nutrition?

Chunks of food in the diapers is completely normal, nothing to be worried about - even as adults we sometimes encounter this. It just means that his body is adjusting to solids. It will happen less often as baby learns to chew foods thoroughly.