It is noteworthy that this incident occurred in Masa Mechasya, and it was there that they spoke begrudgingly regarding the citizens of Pumbedisa.
The Gemora (Kerisus 6a) cites several teachings that Rav Mesharsheya told to his son. One such teaching was that it is better to dwell in the garbage heaps of Masa Mechasya than in the mansions of Pumbedisa.
What did Rav Mesharsheya have in mind? Rashi (Horayos 12a) states that in Masa Mechasya, there were Torah scholars who had the ability to answer Halachic questions and they also had exemplary midos. The scholars in Pumbedisa, however, did not excel in midos tovos, and therefore Rav Mesharsheya warned his son not to learn with them.
Reb Yaakov Emden cites our Gemora as proof that the Jewish population of Pumbedisa was known to be plagued with swindlers and cheats. Accordingly, perhaps we can say that Rav Mesharsheya was telling his son that Pumbedisa might not be the best location for one to reside in.