First, the speaker argues that the dense jungle did not deter the rise of a large civilization. This is supported by the fact that despite of a countless number of vegetable groups, there would be some sort of organizing system. Thus, the founding of large towns indicates that people worked together in order to build expansive constructions. This casts doubt on the reading passage's claim that the high concentration of vegetation would have disturbed the birth of large civilization.
Second, according to the lecturer, it is a biased idea that simply tools have found in Amazon are evidence of primitive civilization. This is because there are another proofs which are much more advanced, such as delicate potteries and beautiful vases. They seem to require a high expertise in order to be made. This refutes the reading passage's assertion that ancient inhabitants of the Amazon consisted of only rudimentary societies.
The final point that made by the lecturer is that European expeditions are not sufficient to conclude that no large civilization existed there. The reason is that there is still unearthed portions of the Amazon. In addition, there is a case in which a place once had been considered just jungle have been identified as a big civilization. This counters the reading passage's argument that there is nothing more than just small, scattered societies and dwellings.