It’s lighter to carry dehydrated carbs than most protein sources. Rice and ramen are tantalizingly lightweight, especially for longer carries. Unless you can live on protein powder, carrying protein will always be heavier.
It might be true that, compared with ‘pure’ carbs like rice and ramen, foods that are very high in protein often holds more water (and so is heavier). If those are your options, that explains the claim that protein is heavy.
But it’s a misconception that rice and ramen are lightweight foods. Ramen is ~350kcal/100g. Nuts, seeds, peanuts, almonds are 550+ kcal/100g. For 4000kcal/day you can take <750g of mixed seeds and nuts or >1,100g of ramen. On a site where people will cut their toothbrush in half to save <10g, that’s an absolutely insane weight savings. I know noone(?) is eating only ramen or rice, so real world savings are less than that, but easily in the 1kg/week range. Ultralight food is high fat, low carb.
Again, I’m in no way trying to knock the general idea of the article – a fish you catch is lighter than anything you bring, it is healthy and a great meal. It’s just that some of the statements in the first few paragraphs make what seems like really weird claims to me:
Carbs and fats are pretty efficient in terms of both calorie-to-weight and calorie-to-volume ratios: cous cous, rice, tortillas, chocolate, chips, nuts, oil, etc.
Carbs are demonstrably bad in calorie-to-weight with an ideal maximum of 400kcal/100g (~350 for rice etc). Contrast that to the second half of the list – chocolate/chips/nuts (~550), oil (850+). Nuts aren’t as high in protein as say jerky, but if they’re a main source of energy (instead of say rice), it seems unlikely you should be struggling to get enough protein.