That complex behaviors can arise from simple processes is understood. Moreover in the species mentioned in the article, the problem spaces relevant to survival

That complex behaviors can arise from simple processes is understood. Moreover in the species mentioned in the article, the problem spaces relevant to survival may have been relatively stable for untold amounts of time. The stable problem spaces increase the evolutionary fitness of efficient algorithms that solve that problem space with min energy expenditure. But such efficiency usually has a cost: reduced flexibility to changes in the problem space. I submit to you that behavioral flexibility in new environments may well correlate with brain size, even excluding humans from the analysis.