Your vegan friend has a good point. Production of animal-based foods typically use 2-10 times more feed (and consequently more land etc) than what would be needed to feed humans directly.
The article cites the often-cited FAO claim [1] that 70% more food production is needed by year 2050. But researchers are now also increasingly agreeing that dietary choices should be considered -- FAO's "70% increase" claim builds on their projections of future human diets.
For a recent example of this alternative view, see Tilman and Clark (2014) [2]. In summary: Current western diets are harmful for the planet and for human health, so let's also consider changing our diets.
The article cites the often-cited FAO claim [1] that 70% more food production is needed by year 2050. But researchers are now also increasingly agreeing that dietary choices should be considered -- FAO's "70% increase" claim builds on their projections of future human diets.
For a recent example of this alternative view, see Tilman and Clark (2014) [2]. In summary: Current western diets are harmful for the planet and for human health, so let's also consider changing our diets.
[1] http://www.fao.org/news/story/en/item/35571/
[2] www.nature.com/articles/nature13959 behind paywall, but also on SciHub http://sci-hub.cc/10.1038/nature13959