דרבי יהודה אדרבי יהודה לא קשיא באתריה דרבי יהודה חמירא להו שביעיתThe apparent contradiction between the positions of Rabbi Yehudah are not difficult, for in the locale of Rabbi Yehudah [violation of the laws of] Shemittah was considered very severe.
In other words, Rabbi Yehudah felt no need to legislate in a case of accidental planting (where one thought it was a non-Shemittah year) because in his community, violation of Shemittah was considered such a terrible act, that no one would do it on purpose. Hence, there's no reason or need to legislate שוגג אטו מזיד.
Then, the Gemara tells a troubling story to illustrate just how serious people took the violation of Shemittah:
דההוא דאמר ליה לחבירו דייר בר דיירתא אמר ליה אנא לא אכלי פירי דשביעית כוותךFor there was a certain man who said to his friend [in an attempt to insult him], "You are a convert the son of a female convert. The man retorted: At least I don't eat the fruits of Shemittah like you!
Apparently, it was considered worse in Rabbi Yehuda's community to eat the fruits of Shemittah than to be a convert the son of a female convert! Moreover, someone in the Daf shiur last night pointed out that in Rabbi Yehuda's time, Shemittah was no longer a דאורייתא - a Torah law. It was by then exactly like it is today - a דרבנן - a rabbinic law. Yet, the people in that community still treated the rabbinic law as if it was still a D'oraita!
Reading the story, I found the whole exchange both terribly troubling but familiar. Why were the same people who were so meticulous about adhering to the nuances of the ritual law of Shemittah so callous about insulting someone else in such a demeaning and inappropriate manner? Why do the two somehow seem so often to be connected to each-other? Is there some link between over-meticulous observance of ritual law and laxity with regard to mitzvot bein adam l'chaveiro?
Reading the two short vignettes connected in the Gemara, it seems that they are indeed linked.