Question

Rabbi Eliezer Melamed writes in Peninei Halakha, “The Four Portions”: On those Sabbaths when these portions are read, two Torah scrolls are taken out. From the first, seven aliyot are read from the weekly Torah portion, and from the second the maftir reads the special portion. Since the haftarah from the Prophets needs to deal with what was read in the scroll to which the maftir was called up, on those Sabbaths the haftarah deals with a matter connected to those portions that were read from the second scroll, and not with the weekly portion that was read from the first scroll.
 
I understood him to be explaining that the reason for this is that the haftarah that is read must belong to the portion that was read from the Torah scroll, and since if they were to take out only one Torah scroll they would also read from it the regular portion that is read every week, therefore a second Torah scroll has to be taken out, so that only the portions read in Adar are read from it alone. But my study partner understood—and this is also how the rabbi explained it—that they take out two Torah scrolls because of burdening the congregation, and Rabbi Melamed is only explaining here how the sequence of things developed. How does the Rabbi understand his words? And what is the law?