Click on the link. See the section labeled "Book Description". The first paragraph following that label ends "It offers two specific reasons for this claim:"
And true enough there are two numbered point which follows. But they are not "two specific reasons". They are together one reason.
Let me illustrate what I mean by that:
Let's say I'm accused of being an axe murderer. In my defence I can offer the following argument:
1; i have proof that I was far away a few hours before the murder 2; the distance between where I was and where the murder happened is such that I couldn't possibly be there in time.
This is not two reason. This is a two sentence argument, and one reason. Let's see an example with two reasons:
1; I was far away from the crime scene, see proof... 2; I don't have arms, thus even if I were there I couldn't possibly wield an axe.
These are two separate reasons.
Why is this thing important? For two reasons:
Before I part with my money, and a substantial chunk of my free time, to read their argument I have to ascertain that they are worth this investment. To do this they have to signal in various ways that they are serious people and not bozos. Having impeccable book description would be in their favour in that department.
The second reason is even more important: If they truly would have two independent reasons to support their argument that would make it stronger. Even if they make some mistake in one, the other might still stand.
As it is now (based on the description and their first chapter exceprt) this is how their argument stands:
their thesis: artificial intelligence that could equal or exceed human intelligence is impossible.
1; The only way to engineer such technology is to create a software emulation of the human neurocognitive system.
2; To create a software emulation of the behaviour of a system we would need to create a mathematical model of this system that enables prediction of the system’s behaviour.
3; It is impossible to build mathematical models of this sort for complex systems.
These points form a chain. If any of these points is false, their argument fails. Thus they don't have two reasons, they only have one reason.
And I have serious doubts about every single of those statements alone. Which makes their arguments super shaky.
I will be nitpicky here. They say they will offer two specific reasons. But they don't. They write one reason, which has two predicates. The two points make up together one reason. The two points are not reasons in themselves, only together do they form an argument.
Obviously this is not a substantial critique of their argument. But it is quite telling that even in their description, which should be the best edited and most polished part of their book, they write sloppy things like this.