I don't know who said that, but sounds like how a scientist would characterize a historian's criticisms of guns, germs, and steel, although maybe I could imagine a cultural historian saying that if he was pressed for time. But environmental history is a big part of the discipline, and many, including luminaries such as Donald Worster, argue that culture is an adaptation to nature.
The criticism of GG&S, as far as I know, come in three veins.
One, geographical determinism obscures the consequences of human decisions. From this perspective, every shitty thing that has ever happened in history, from slavery to imperialism to genocide to environmental degradation, was preordained in the shape and composition of the continents, thereby absolving all the individual and collective actors responsibility of their conscious decisions.
Second, a huge amount of criticism has come from specialists noting the voluminous errors in GG&S on the many different regions and periods it tries to cover.
Third, there are those who say that much of the science and geography in GG&S is wrong. Just to provide a few examples from James Blaut's critique in Eight Eurocentric Historians, Diamond argues that agriculture was productive in Eurasia because it had a common temperate climate along an east-west axis which allowed diffusion, ignoring the fact that most of Eurasia is desert and inhospitable mountains, that diffusion very commonly took place on a north-south axis (think of corn being domesticated from Canada to Peru, wheat from northern Europe to Ethiopia, rice from northern China through southeast asia), and that when there was incentive, crops could be easily adapted to different environments (think of the potato and sweet potato, both domesticated in tropical climates and spread to cold and seasonally dry areas). He revives the long-debunked argument that China became a despotic empire because of its unified geography, in contrast to Europe, which could not be unified because of its indented coastlines. This ignores the fact that it was Southern Europe with the peninsulas and separate geographic cores. The region responsible for most of the major developments in the last 500 years, including the industrial revolution, was Northern and Western Europe, which is mostly flat, with the Northern European Plain stretching from France to Russia and from France almost to the Spanish border. The boundaries of most of the nation-states that formed in this region do not reflect topographic barriers. His assertion of Chinese stagnancy in the early modern period is also decades outdated and discredited.
The popularity of GG&S highlights the tension between the hard and social sciences, as well as the pretensions of the populizers of the former. Why is it that despite all of the inaccuracies pointed out by various specialists this book is still so highly regarded by the general educated public and by those in the sciences? I think it is because the book purports to be "scientific," in contrasts to the works of those woolly headed specialists in the social sciences. Therefore, the information in the book occupies a higher plane of knowledge than that produced by the specialists. As Blaut put it, Diamond's argument is "scientistic" in that he "claims to produce reliable, scientific answers to [historical] problems when in fact he does not have such answers, and because he discards wholesale the findings of social science while inserting old and discredited theories of environmental determinism."