Q. Can people who didn’t learn join in a suyum and eat meat?

A. Remoh (O.C. 551:10) rules that when someone finishes a tractate of the Talmud and makes a siyum, he can eat meat and drink wine on the nine days and the ones that belong to the banquet may join him, even though they did not participate in the learning, Mishna Berura (ibid. 75) explains that those are the people, related to him or his friends, that would have come to the siyum, on any other occasion and not only during the nine days. (see also; Talmud Shabbos 118b). Some Poiskim require an actual invitation, (Oilas Shmuel 56 – Hisorerus Teshuva 1:104 and Mekadesh Yisroel, Bein Hametzorim 136).

Horav Shlomo Miller’s Shlit”a opinion coincides with the above, however he does not require one to actually be invited.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a