A mishnah on today’s daf explains the specific procedure through which courtyards off an alleyway can be merged together for the purposes of eruv:
How does one merge the courtyards that open into an alleyway? One places a barrel filled with one’s food and says, “This is for all of the residents of the alleyway.”
Bringing food for shared consumption into the alleyway establishes residence in the alleyway for those whose homes are in adjacent courtyards and the declarative statement designates the food for this purpose.
But one more step is required. For the merging of domains to become operative, another resident must take possession of the food on behalf of everyone who lives there. Rav Yehuda explains:
The barrel that is used to merge the alleyways must be raised a handbreadth from the ground.
In talmudic times, the act of lifting was considered a form of acquisition and so the lifting of the barrel was required to formalize the transaction which would merge the domains.
Rav confirms Rav Yehuda’s teaching:
The elders of Pumbedita stated these two matters. One was this teaching about the barrel. The other was: with regard to kiddush over wine on Shabbat and Festivals, if a person tastes a mouthful of wine, they have fulfilled their obligation; if not, they do not fulfill their obligation.
This happens a lot in the Gemara — we are suddenly given a collection of thematically disparate teachings that were all taught by the same group of people. It can lead us to suddenly veer off topic, as in this case from eruvim to kiddush. If this seems a strange way to organize material, consider that the Gemara, in its origins, was a set of oral teachings passed down by rabbis committed to preserving the names of sages alongside their teachings. It makes sense, then, that teachings associated with the same named source tended to be grouped with one another.
On the other hand, maybe there is a connection between the raising of the barrel that finalizes an eruv and making kiddush. Back on Berakhot 51 we read this:
And one lifts the cup at least one handbreadth from the ground. Rav Aha, son of Rabbi Hanina, says: What is the verse that proves this? I will lift the cup of salvation and upon the name of the Lord I will call. (Psalms 116:13)
Rav Aha’s prooftext demonstrates that we raise the kiddush cup before invoking God’s name when we recite the blessing of kiddush (i.e. our practice follows the order of the verse). Just as raising the barrel indicates that it is our intention to take possession of the food contained within, raising the kiddush cup signals our intention to sanctify Shabbat.