Question

Rashba, in Tosafot on Bava Batra, writes that inheritance by way of transmission through an intermediary operates such that the intermediate deceased heir inherits and then passes it on to his own heir. In the case there in Tosafot, the son inherits from his deceased mother, who inherits from his deceased grandfather, who inherits from his son.
They challenge this from later in the tractate, where it says, “Perhaps he can say: I come by virtue of my grandfather’s father,” regarding one who inherits his paternal grandfather. That implies that inheritance through this kind of transmission is directly from the original decedent.
In She’erit Yosef it is answered that according to Rashba both modes are correct, and the heir chooses in which way he wants to inherit it. For example, if his father sold his own father’s property, the heir would not want it to pass through the father, because then the inheritance would go to the buyers.
In my opinion this explanation is strange. Why should such an option exist? If both modes of transmission exist in this type of inheritance, then both should take effect, stringently.