Commentary for Avodah Zarah 112:5

Again, according to the mishnah it would seem that Jews and idolaters can press wine together. And thus, in the Babylonian town of Nehardea they do so. But the question is put to Shmuel whether this wine it is permitted to sell or drink this wine and he delayed three festivals before answering.

The Talmud now tries to figure out why Shmuel had to delay three festivals before answering. The first reference point is a baraita in which R. Natan and the other sages (later assumed to be R. Shimon) argue about a case where an idolater measured the amount of wine in a vat with his arm or leg. Clearly in such a case the idolater did not intend to libate the wine. Nevertheless, R. Natan says that if he touched it with his hand, it is prohibited to derive any benefit from the wine. The sages say it may be sold, but they agree that it may not be drunk.
The problem is that even if Shmuel holds like R. Natan, it is prohibited only if he touched it with his hand. The people pressing the grapes touched it with their feet only. So even if he held like R. Natan, he should have allowed them to sell it.