Not sure why the person you’re replying to is refusing to explain. Assuming they’re not a TOTAL idiot, I’d guess they’re alluding to a baking rule of thumb for mixing order. Maybe they learned this rule but they don’t actually understand it well enough to talk about it?
Generally, you include sugar with the “wet” ingredients while baking. It’s a timing thing, it tends to incorporate better and dissolve a little if you mix it with your butter, oil, milk, eggs, etc. Once that’s all mixed in you add your “dry” ingredients like flour and baking soda / powder. Those are easy to over mix so you add them last minute.
Sugar is not a liquid ingredient, it’s just a rule of thumb, the person you’re replying to is being annoying.
Banana does get a little gluey when cooked. It’s not a perfect substitute but it does help keep things together a bit.
Source: rolled oats + mashed banana + chocolate chips makes a decent chewy cookie.