Judging In Accordance With Persian Law

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I saw this a bit back, and decided I wanted to mention it. A fascinating gemara. I cite from my Rif blog:

{Bava Kamma 58b}

ההוא גברא דקץ קסבא מחבריה
אתא לקמיה דריש גלותא
א"ל דיינא לדילי חזיין לי תלת תלת בקינא הויאן ושויאן מאה זוזי
זיל הב ליה תלתין ותלתא ותילתא
אמר בהדי ריש גלותא דדאין דינא דפרסאי למה לי
אתא לקמיה דרב נחמן
א"ל בששים

There was a certain person who cut down a date-palm of his neighbor. He came before the Exilarch. He said to him: 'I myself saw the place; three date-trees stood close together in one nest and they were worth one hundred zuz. Go therefore and pay the other party thirty-three and a third {zuz}. He {=the defendant} said to the Exilarch: 'What have I to do with an Exilarch who judges in accordance with Persian Law?'
He came before Rav Nachman. He {=Rav Nachman} said: In conjunction with 60 {times as much}.

{Bava Kamma 59a}

רב פפא ורב הונא בריה דרב יהושע עבדו עובדא כוותיה דרב נחמן בששים
איכא דאמרי הכי שמין דיקלא אגב קטינא דארעא בששים
והלכתא כוותיה דרב פפא בדילקא ארמאה
והלכתא כוותיה דריש גלותא בדיקלא פרסאה:

Rav Pappa and Rav Huna son of Rav Yehoshua acted in practice like Rav Nachman, in conjunction with 60. Some say so did they assess palm tree in conjunction with the small piece of ground, in conjunction with 60 {times as much}.
And the halacha is like Rav Pappa by an Aramean palm, and the halacha is in accordance with the Exilarch by a Persian palm.

In the actual gemara, the juxtaposition is not that stark. But the Rif places them together, skipping over a bunch of intervening gemara. See here fo

As Soncino explains, in accordance with Rashi on the daf:

an Aramean palm: Which is by itself of no great value.
a Persian palm: Which is even by itself of considerable value.

But is that indeed the reason for the Resh Geluata's ruling, that he was dealing with a different sort of tree? And since it was in Persia, it was a Persian palm? If so, why did Rav Nachman rule otherwise? Pashut Peshat would seem to be that he was judging in accordance with the actual law of Persia, which was then the litigant's complaint.

Rashi and Tosafot differ on this.
Rashi writes correctly:
דינא דפרסאה - שאינו דין תורה:

And Tosafot do not really argue, but offers an alternate explanation that some say, which could work:
דדאין דינא דפרסאה. י"מ של דקל פרסאי דאמר לקמן הלכתא כוותיה דריש גלותא בדקלא פרסאה ולפי מה שפירש בערוך דקשבא דקלא פרסאה אי אפשר לפרש כן:

Regardless, there is a tension here. The obvious answer, to my mind, is that the Resh Geluta indeed was judging Persian law, being an appointee in Persia. It is an interesting source for judging in Jewish courts the dina demalchuta. But halacha, when not going according to the dina demalchuta, is not as he ruled. And when it came down to the hilcheta, well that is not a statement from a named Amora. Rather, it is the anonymous setama degemara, acting on its own initiative to harmonize, and taking its cue perhaps from the detail of אגב קטינא דארעא, and reading in a difference of the type of palm tree.