Hi Etsevdos,
The reason why (B) is incorrect here is that you do not have any information about what the political economists mentioned in the first line think about human indicators. The most you can really infer from the passage is that they are not a part of their initial calculations regarding the health of a nation. And certainly, the fact that there is some short, dismissive consideration offered beginning on line 19 does not allow you to infer that they think it is "irrelevant." We don't know what they really think of it, but they do acknowledge its existence.
Moving on to why (A) is correct, lines 19-23 really do support the interpretation of "similar" that is stated in the answer choice. as far as political economists go. Of course, the author goes on to indicate why that is the wrong view, but as far as the political economists are concerned, they think if GNP goes up, so do the other indicators. That's why it's correct.
Thanks for the great question and I hope this helps.