In Solasta, backpacks are worn items, and magical versions, in the vein of bags of holding exist- reducing weight by a certain %.
Cant care less about what they do in some completely different game. :-/
He was answering the question posed by the person you had just agreed with. They asked how, unless it's a magical item, backpacks can be a weight reduction item. You said "Agreed" to that question, and then Anfidel gave an answer to that question.
As for whether or not care about what they do in Solasta (thank you for saying that you CAN'T care less, it kills me when someone says they CAN care less) that's fair, you don't need to care, but I would argue that the existence of Solasta is a rare opportunity for comparison, as these are two games, both in early access, both using the same baseline rules system to emulate the same game. I think comparing the two games and considering what does and doesn't work is a worthwhile endeavour, if for no other reason that it can help zero in on what could be causing frustrations for players. I think both games are trying to be different things in a lot of ways, but ignoring points of comparison feels like the wrong way to go all the same.