Shabbat daf 9: Bavel vs. Eretz Yisrael regarding the start of the meal

On Shabbat daf 9:

And when is the beginning of eating? Rab said: When one washes his hands; R. Hanina said: When he loosens his girdle. But they do not differ: the one refers to ourselves [Babylonians]: the other to them [Palestinians].¹⁶  Abaye said: These Babylonian scholars, on the view that the evening service is voluntary,¹⁷  once they have undone their girdle [to eat], we do not trouble them;¹⁸  but on the view that it is obligatory, do we trouble them? 

There is a machlokes between Rashi and Rabbenu Chananel as to which is the lan and which is the lehu -- which practice is that of the Babylonians and which of the residents of Eretz Yisrael. Rashi says that the loosening of the girdle is the Babylonian custom. Thus:

Rashi: the Babylonians were tightly belted, so they loosened the girdle before eating; but for the Palestinians this was unnecessary. R. Han. reverses it.

Indeed, we see elsewhere that wearing the girdle was a Babylonian practice. On the other hand, consider that Rabbi Chanina was an Amora of Eretz Yisrael. Back on the first hand, consider that Rabbi Chanina was not an Amora of Eretz Yisrael, but a Babylonian who traveled there. So was Rav. Also consider that Abaye rather explicitly associates the girdle with the Babylonians. And Rabbenu Chananel does not only reverse it, but gives both as options. (See on the daf itself.)

We can bring in the Yerushalmi (Shabbat 7a), and see for ourselves that they exclusively say washing.

ולא לאכול.  התחלת אכילה.  איזו היא.  רב אחא רבי בא בשם רבי משיטול ידיו.  רבי אחא אמר לקידוש איתאמרת.  רבי בא אמר לברכה איתאמרת.  רב נסב לידוי רמז חייא בריה למזוגא.  בעא מיתן ליה.  אמר ליה כבר התחלנו בסעודה.  דילמא ר' מיישא ורבי שמואל בר רב יצחק הוון יתבין אכלין בחדא מן כנישתא עילייתא.  אתא ענתא דצלותא קם ליה רבי שמואל בר רב יצחק מיצלייא.  אמר ליה ר' מיישא ולא כן אלפן רבי אם התחילו אין מפסיקין.  ותני חזקיה כל מי שהוא פטור מן הדבר ועושהו נקרא הדיוט.  א"ל והתניא חתן פטור.  חתן אם רוצה לקרות קורא.

As for myself, I am not so convinced by the gemara's ha lan ha lehu. It sounds like something the gemara intuited for itself from Abaye's following statement, that it is particular to Babylonian scholars, and then applied the idea of ha lan ha lehu from elsewhere. But Abaye is only ascribing the position of maariv as a reshus to those of Bavel, not the girdle.