This is premise. The author uses (A) to support the claim that the similarities between the products aren’t coincidental.

The author never says this. She doesn’t address why the products are similar (who copied whom, or if the companies colluded), she only denies that it’s coincidence.

This is exactly what the author concludes. The argument supports the claim that the similarities are not a “mere coincidence” by giving examples of similarities too fundamental to have occurred accidentally.

This isn’t stated in the argument. We don’t know whether the author believes this could be a plausible explanation in some cases. She’s only concerned with addressing this specific case.

The author doesn’t say this; she doesn’t discuss anything appearing to be unique. She’s concerned with rejecting the idea that these similarities are coincidence.