The author doesn’t suggest that the claim goes against our common-sense intuitions. So there’s no support for the claim that the author’s purpose is to provide an example of something counterintuitive.

This best captures the author’s purpose. The author makes this assertion to support the claim that “[software programs] fall more appropriately within the established domain of copyright law.” Copyright law protects “only the particular way in which the underlying ideas are expressed.” So if software programs are an “expression of ideas in the form of specific texts,” this fact supports the claim that copyright law should protect software programs.

The author isn’t trying to provide a causal explanation of a phenomenon (a thing or event that happens in the world). There is no phenomenon discussed in this part of the passage. Whether software programs should get copyright protection isn’t a phenomenon; whether they should be patentable isn’t a phenomenon. Furthermore, the claim that software programs constitute an expression of ideas doesn’t tell us the cause of something.

The author’s assertion is part of the author’s argument. It’s not an attempt to help laypeople understand a term. Although the author elaborates on the meaning of “specific texts,” that elaboration is part of the author’s attempt to show how software programs constitute expression of ideas and therefore deserve copyright protection.

Although there may be support for the idea that both the author and the patent proponents believe software programs are expressions in the form of sequences of code, the author’s purpose isn’t to show a point of agreement. The assertion helps support the author’s own view that copyright law should protect software programs.