פירוש על עבודה זרה 70:15

The Talmud here quotes another sugya from Tractate Hullin. In this sugya Shmuel interprets a mishnah such that it states that any rennet (the stomach enzyme) taken from an animal that was not slaughtered properly is prohibited. So how could he here say that the problem is that the skin of the stomach is the problem.

The sugya begins with R. Yohanan noting that bread was not permitted by the “court,” which seems to be some sort of official court composed of the sages. The implication is that there were others who did permit bread made by Gentiles. And indeed, the Talmud shows that some people mistakenly thought that Rabbi [Judah Hanasi] permitted bread made by Gentiles.
In reality, Rabbi only wanted to permit bread “in the field,” meaning in a non-social situation. Eating Gentile bread was prohibited because it leads to fraternization (breaking bread with someone is a sign of socializing), and in the field there is no such concern. But Rabbi did not mean to permit such bread under all circumstances.